I had the same experience years ago while riding a double century on my flat bar road bike. It only effected my right hand though. It took about a week before I was really able to grip things. I couldn't brush my hair or teeth using my right hand or even zip up my zipper (try zipping your jeans with your left hand...not easy). I haven't had the problem since I switched to a regular road bike. I think it helps being able to switch positions with your hands while riding.