I've done the exact same! There was an old abandoned psych hospital that had asbestos in it, and I went exploring in it, at least 2-3 different times, for about 5-6 hours at a time! When we went into the tunnels, or really musty areas we put our shirts over our noses & mouths, and we're still ok. I've never had asthma, and still don't....it probably wasn't the GREATEST idea, but it was really fun, and we were as safe about it as possible.
Isn't it so fun to explore places like that? I just love to take pictures & stuff, and it almost reminds me of being in a scary movie! Too bad the place I went exploring in is torn down now.

If you start to feel REAL awful for more than a week, go see a doctor, but you're probably fine.
(Have the pics posted somewhere?)
