An intruder in my apartment gave me PTSD symptoms for months. Here's what people get wrong about being 'triggered.'

• A few years ago, I had an intruder in my apartment, and after he had gone I suffered hypervigilance — a symptom of PTSD.
• For months, I felt a sense of real and immediate danger any time I was indoors alone, even though I knew I was safe.
• Because I lived alone, I ended up couch-surfing for several months, but adapting my life to never being alone was extremely difficult.
• I never sought a formal diagnosis of PTSD, but I asked an expert to talk me through what happens in the brain during an encounter that causes it.
• Trigger warning: This story contains descriptions of violence and trauma.

One day about three years ago, I found an intruder in my apartment. The encounter was shocking, but brief — so I never thought it would affect my life the way it did.

I had believed I was alone and safe at home, but within thirty seconds a man had pushed me to the floor, and I thought I would be raped or killed.

Being nervous after a shock is natural and normal. What is not normal was the hypervigilance I experienced for months afterward — a sense of immediate danger even when I knew I was safe.

It's one of the numerous symptoms of Post-Traumatic Stress Disorder (PTSD), and it turned my life upside down.

I'm mostly ok now. Years after the incident I talked to Prof. Neil Greenberg, a defense mental health specialist at King's College London, about how the brain works in situations like this, and why some people live with trauma afterward.

We commonly assume that PTSD is just the result of a scary encounter, and mainly affects people in military service. But as Greenberg told me it can affect people in numerous situations — from reporters working in war zones to healthcare workers — and much more specific factors dictate whether or not you'll experience PTSD.

Here's what happened to me.

An intruder was there the whole time I thought I was alone

I came home from work and locked the door behind me. I lived alone, and I'm the type to exploit that luxury to the max — which means peeing with the bathroom door open, shedding my bra, and repeatedly asking the cat why she's so fluffy. I cooked dinner and relaxed into a lazy evening.

I'd just started an HBO drama when I paused it to get something from my bedroom.

On the way there, I heard an unmistakably human sound. I can't remember what it was — a cough, a shuffle, clothes rustling? — but it was right there with me. I stood there a beat. A dark shape entered the hallway.

Both of us ran for the front door, but he got there first. He pulled a coat from the hook, threw it over my head, and muzzled me with his hand. I crumpled like a leaf.

Pressed to the floor with the coat over my head, next to my own front door, was the exact moment I expected to be raped or killed. The next moments would define whether I lived or died, and I can still feel the place at my waist where I anticipated a knife's point.

I didn't realize it, but I was screaming. I also didn't realize that he was asking me to stop.

In fact, he was shushing me. And was telling me he was leaving, but he needed me to stop screaming first.

To this day, it remains the best deal I have been offered in my entire life.

I formed my hands into a prayer, stopped screaming, and he was gone.

I was safe. But I wouldn't feel that way for a long time

The whole thing took less than 30 seconds. Aside from a slight bruise on my lip, I was uninjured. Nothing had been stolen. I began to think I had escaped unscathed.

Piecing it together, I worked out that he had already been in the apartment when I came home. It was likely an opportunist would-be thief who found himself in too deep, and I caught him trying to sneak out.

It was at that moment hearing the noise in the hall that a very ancient part of the brain was activated, Greenberg explained to me.

"There's a bit of your brain called the amygdala, which is all to do with threat control," he said. The amygdala assesses threats without needing conscious thought. This means that even without knowing why, you are "instantly put on alert" by an unexpected noise, as he put it.

That alert is sent to the ventromedial prefrontal cortex — which deals with emotional processing — and the hippocampus, which is broadly to do with memory. Both of those parts rifle through your past experiences to figure out if this threat is actually something explainable.

And normally, it is. "You look over, and it's a twig, or there's a rabbit, or whatever," said Greenberg.

But in my case, there was no good explanation. "That bit of 'how the world should be' was strongly challenged, because there was a person there when there shouldn't have been," said Greenberg.

In many cases of PTSD, the way these parts of the brain interact is altered by the incident, meaning they don't function normally for some time after. PTSD UK — a charity set up to help sufferers — emphasizes that the condition isn't a mental illness, but a psychological injury.

While people can go through a scary situation and emerge with nothing more than a healthy sense of caution, some events tip people over the edge into PTSD. The difference, Greenberg explained, can be in two factors.

"One of the key aspects about traumatic situations is you perceive them as being both threatening and out of control at the same time," he said.

If the front door had been wide open when I got home, I'd have had the chance to investigate the danger from a safe distance — so it would have felt scary but somehow within my control, he explained.

And if the uninvited person had actually been part of a surprise birthday party, it might have made me jump, but it wouldn't have been threatening.

It's the combination of the two that often causes the injury, said Greenberg.

(Note to friends: Do not organize me surprise birthday parties.)

After that, I didn't know how to feel safe

In the days and weeks that followed, I never felt safe alone. It didn't matter how many new locks I added, or how often my friends helped me check every nook and cranny.

As soon as my back was turned, the guarantee expired, to be replaced by an overwhelming sense of immediate danger. It was like playing whack-a-mole with my psyche.

I desperately wished for X-ray vision, so I could see through the walls of my apartment and into every room all at once. Then, I thought, maybe I could relax. (As long as I didn't sleep.)

Yes, I understood that in a technical point of fact it was impossible for someone to be hiding there. But the nearest analogy I can give you is this.

I don't know if you've ever thrashed in frustration at the cliche of the teen horror movie, where the characters insist on exploring a haunted house when it's obviously dangerous.

Watching, you want to yell at the oblivious teens, because in reality, nobody in their right mind would press on, and they're only doing it because it's a stupid movie and the plot depends on it.

That was my amygdala, which was yelling at me in totally ordinary situations, all the damn time.

This is because what happened made no sense

An intruder had appeared when I felt assured I was alone. The "impossible" had happened, and I could no longer trust the evidence of my senses.

The fact that he was already there, when I assumed the apartment was empty, set up what Greenberg called "cognitive dissonance."

Ordinarily, after a dangerous situation, people have an adaptive response, he said. The body has been alerted to danger, it's prepared a fight-or-flight response, and you win or lose that encounter.

We then adapt our belief system to account for it. Dogs sometimes bite, soup can burn your tongue. But for me, the new belief system was: your apartment sometimes has an intruder hidden in it.

"In this situation, you couldn't make sense of it," he said."The brain tries to set up two things: 'This is how the world is, which is safe and I'm in control of it,' versus 'this is actually what happened. It wasn't safe.'

"And when you can't reconcile your view of how the world should work with the facts in front of you, you enter cognitive dissonance."

I was withdrawn, jumpy, and craved to be alone. But I couldn't.

The only way to feel at ease was being around other people, but I wasn't exactly feeling sociable.

Normal life disappeared. Several friends with spare rooms gave me keys to their apartments, and were amazingly supportive and patient. But when they weren't home, I would have to grab my things and move on.

I organized my entire life around where other people would be. As an introvert who hates planning, this is basically my personal Bad Place.

I was usually too proud to ask people to stay home so I could feel safe in their apartment, and when they did, I felt like a parasite. I usually just retreated to the spare room, pretending I was getting the alone time I craved, but feeling like a ghost in someone else's life.

I had no space to cook a meal or choose what to watch on TV. Doing laundry, getting my work wardrobe together, and feeding my cat were a logistical nightmare. I felt vulnerable getting to sleep, and was always in different beds, so I was tired and disorientated at work.

Seeking nonexistent relaxation and the company of strangers, I inevitably spent more time in bars. Wine, supposed to relax me, didn't. Although I gave it a good try.

If I really felt like I'd outworn my welcome, I would walk the streets in the middle of the night.

Exhausted, I'd often try to go into my apartment, and would stand outside the door to build up the courage. But it was as though an invisible intruder had moved in, and we couldn't cohabit.

I'd startle easily, and at times I'd be scared even with company. One time, I had to stop a boyfriend from slicing a watermelon for us, because I couldn't let him handle a knife near me. We had to leave the flat and go for a walk so I could calm down.

Being 'triggered' is not what most people take it to be

After months of this, I slowly, slowly regained my independence. The morning I woke up after a whole night alone in my flat was a victory. But even much later, triggers remain. I still startle at a strange noise, and during the coronavirus lockdown in the UK I've been checking my apartment several times a day.

One night, some weeks after I felt better and I was staying with my parents, I woke in the night to an inexplicable noise. While one part of my brain knew it was the cat trying to get out, another part had me convinced: It was happening again. An intruder was in the house.

Before I was even awake I had thrown myself out of the bedroom window. Thankfully, there was a roof below. It was 4 am on a freezing night before New Years' Eve, and my mum was on the point of calling the fire brigade before we figured out how to get me down.

Believe me, I didn't want to be there: but that's how triggers work.

"Triggered" has become a catch-all term in people's lives: a reference for experiencing a strong memory, or an alt-right term in the ongoing culture wars. It crops up in the title of Donald Trump Jr's book "Triggered: How the Left Thrives on Hate and Wants to Silence Us" as well as a popular conservative podcast.

It's long been used — along with the term "snowflakes" — to mock people calling for warnings on material that could potentially set off a trauma response.

While I get that not every potentially triggering stimulus can be accounted for, people who get genuinely triggered are dealing with something far tougher than a matter of their personal attitude to the world. And they have absolutely no choice in the matter.

If anything, the person with PTSD is the opposite of a snowflake: They're actively facing down an uncontrollable reaction at all times. As a form of psychological injury, PTSD can't be chosen, or persuaded not to happen, or toughed out.

"A trigger is something that turns you into a bag of jelly, because you can't stop your anxiety symptoms," said Greenberg. "You can't stop your body reacting, or your heart pounding like that. That's what a trigger is. It takes you back. It may actually bring flashbacks."

For Greenberg, the main misuse of the term is when it's used to describe sensory associations, such as when we say memories are "triggered" by smell.

But in the medical sense, a trigger "makes you unable to function," he said. It causes physical symptoms such as a racing heart, diarrhea, and sweating over which you have no control.

"The key thing about a trigger is it causes you to be psychologically disturbed by whatever it is that you're experiencing at that time."

PTSD throws a lot at you — but one thing is crucial

Many of the things I went through — withdrawal, numbness, jumpiness, emotional unpredictability, having a bleak sense of the future, poor sleep, and of course, the fear of being alone — are among the symptoms of PTSD.

I don't know if they were a result of my ridiculous new lifestyle, or PTSD, because I never sought a formal diagnosis — like many others, I tried to cope without addressing it. (My conversation with Greenberg did not constitute a diagnosis.)

A primary symptom, Greenberg said, is "re-experiencing" the event through flashbacks or nightmares — which thankfully, rarely happened to me. This isn't just remembering the event, but genuinely feeling like you're going through it again.

You can find a lot more symptoms here.

What Greenberg recommends is addressing it sooner rather than later.

"The real unfortunate stupidity of the situation is that actually most people do only come and get help once they reach a crisis point — once they've lost their job, or they've lost their relationship, or they've had a loss of self-esteem because of the trauma," he said.

The lesson here is: Be a "snowflake." Don't tough it out.