A few times in the past year or two, I've opened an Android application that includes a social component and is connected to my Facebook account and been instantly redirected to either the Facebook app or the website in a browser, had to log in, and was immediately told that my account had been locked due to "suspicious activity" and forced to change my password. After doing so and proceeding to the "review activity" step, there was absolutely nothing suspicious in there, just a bunch of things that I actually did do. I completed the review, confirming to Facebook that everything was legit, but I can't change my password back to what it was before.
The first time this happened, I had to change my password from a the very good one I had been using (memorized, unique to Facebook, no dictionary words, never written down, uttered, or shared with anyone), to another password I had that was similarly secure other than being unique to one account (because it's hard to come up with, and remember, new passwords that meet those criteria). Each time, I become unable to ever use the prior password, even though it's clear that the password was not actually compromised - I never get an alert about a failed login attempt, I never have posts I didn't create or other similar indications of third-party access, etc.
So I have two questions (I know there's an unwritten one-Q-per-post rule, but I think these are closely related enough that it should be acceptable):
Is there any way I can get any of those previous passwords, which were not compromised, unblocked?
Is it actually possible that someone managed to access my account without being detected as an unrecognized device and sending me an alert, nor leaving any trace in the "review recent activity" log, and that they also did not change any of my info or settings, post any spam, or otherwise tip any of my friends off, either?