If you see some suspicious activity there, you can check out your recent account access. Note that since your viewing activity can be modified (you can "x" out certain things), if you think your Netflix has been hacked, go to recent account access even if there isn't unusual viewing.
Here you'll be able to see all the places your account has been accessed from. If you don't recognize any of them, it's likely your account has been hacked.
If it has been there's an easy fix. Navigate back to your settings and choose "Sign out of all devices."
This will kick everyone who is logged into your account off. Then you can change your password, and they won't be able to get back in.
Once you've done that, you should try and figure out how you were hacked. A good place to start is haveibeenpwned.com.
Haveibeenpwned.com gives you a rough idea of whether your personal information has been leaked onto the internet. Last year, when writing about her Netflix account being hacked, a Motherboard writer found that her family’s login info had appeared on Pastebin, a site for dumping plaintext files, in a document with the title “BunchaNetflixAccounts.” The information from 2,400 other users had also been compromised.
My colleague also found out, via haveibeenpwned.com, that some of her accounts had been compromised in a data dump. She then knew it was wise to change her passwords on more than just her Netflix.
