In my reputation dropdown, on the top bar, I see -10 reputation for "user was removed". When I click on it, it links to my own profile page.
Why did this happen?
See What does “user was removed” mean and why did my reputation change because of it? on the main meta. In short, a user who had upvoted one of your answers was deleted, so all their votes were removed as well, so you lost the 10 reputation you'd gotten from their upvote.