Sounds like a pinch flat... You'll know when you look at the tube, it'll have two identical (or nearly so) holes opposite each other... kind of like a snake bite.
I got one the other day when I hit a 1/2" concrete edge WAY too fast.
*** Ha... someone beat me to it... that's what happens when I'm talkin' on IRC and not paying attention!
__________________
"There is no greater wonder than the way the face and character of a woman fit so perfectly in a man's mind, and stay there, and he could never tell you why. It just seems it was the thing he most wanted." Robert Louis Stevenson
