I've been really lucky with my stays.
I guess the worst was when I was on my own, top floor, in London and the fire alarm went off at 1am.
It wasn't busy and I appeared to be on my own on this floor as I navigated my way to the external fire exit stairs. I met one lady popping her head out of the room door and asked if it was for real and she wasn't leaving the room "because her baby was asleep". I offered to help her, but she wouldn't have it. She was staying put!
I went down the fire exit stairs, seemed like forever on my own, and at the bottom it led to a sort of external concrete parking area where the Oxford Steet fire brigade had just arrived.
I was luckily able to tell them, and later someone more formal, that there was a lady in room x with a baby appearing to not be evacuating.
Then we waited for about 2 hours in the cold for them to do their stuff.
It was all OK in the end, but quite a scary experience that I'll never forget.