"I was unwell with post-natal depression, which no one ever discusses, post-natal depression, you have to read about it afterwards, and that in itself was a bit of a difficult time," Diana said during an appearance on BBC's Panorama in 1995.
"You'd wake up in the morning feeling you didn't want to get out of bed, you felt misunderstood, and just very, very low in yourself."
She added that it took her by surprise because she had "never had depression in my life."
"I received a great deal of treatment, but I knew in myself that actually what I needed was space and time to adapt to all the different roles that had come my way," she added.
"I knew I could do it, but I needed people to be patient and give me the space to do it."
When asked by the interviewer what the family's reaction to it was, Diana said: "Well maybe I was the first person ever to be in this family who ever had a depression or was ever openly tearful.
"And obviously that was daunting, because if you've never seen it before how do you support it?" she said.
The princess added that "it gave everybody a wonderful new label — Diana's unstable and Diana's mentally unbalanced."
"And unfortunately that seems to have stuck on and off over the years," she said.