Question says it all.
I've had suggestions of using "relieved" or "elated", but none of them really sound like what I'm thinking of. Think about it this way. The other day, I nearly dropped my laptop while walking to class. My laptop is really, really, pricey, and dropping it would render it into a nice little paperweight.
Luckily though, I caught it just as it was fumbling around in my hands.
I don't know what to describe it as.