This is not nearly as strange as it sounds.... I've had rats sustain severe injuries and even get poisoned and the next day they appeared fine.
Part of this is because rats don't show their weaknesses. Gently feel your rat all over to see if she has any sore spots. You can bathe her to see if any injuries become apparent when her hair slicks down, but that's about all you can do. Also check for any poisons your rat could have gotten into.
The other thing is that 24 hours after each of our rat's near death experiences, they seemed to be perfectly fine... rats tend to either die fast or recover super quickly. There isn't much in between. This applies mostly to young rats though. If a rat survives a trauma for the first few golden hours, it's usually pretty much OK by the next day, so likely you're OK now.
So, I suppose you should look for anything that could have caused a poisoning or injury. Maybe your neighbor's bug bombed their apartment or an exterminator was in your apartment when you were away... I've lost animals to both when I rented years ago. But if you can't find a cause, and your rat seems fine, you are most likely out of the woods. There isn't much you can do anyway, so I wouldn't drive myself crazy with worry.
And by the way... Last year we moved the stove and found a full box of rat poison under it... it was left behind by the former owners of our house, long, long ago and it sat there for decades. Of course our rats played under the stove and luckily none of them ever ate it. We've lived here for nearly 20 years, and most certainly weren't expecting to find this little time bomb waiting for us... We've even replaced the kitchen floor, so how the stuff somehow survived under the stove remains a mystery. It's gone now, but who knows what other dangers are lurking in our home we may not know are there? So it might be a good idea to do a safety check and talk to your neighbors and landlord.
Best luck.
