Ya know, I have had my baby on the bed with me while I was awake, SUPERVISED, and she still has managed to fall off a couple of times. So don't feel too horrible about it, because accidents do happen. Whenever my DD gets a head bump, the 3 things I watch for is 1~ Does she cry immediately, and is she consolable? 2~ I watch her eyes, and pass a light in front of them. If they dialate normally, and at the same speed, I don't worry. If they aren't normal, or if they don't change when I pass the light, I would run her in. 3~ does she otherwise act normal, play, and eat once she has had a chance to calm down? If her balance seems off, she won't eat, or are any other noticible diffences in her then I would also run her in.
Don't beat yourself up too bad. Accidents do happen. As long as you learn from them, you and your DD will be fine. :) BTW.. She has knocked herself silly a lot more often, and a lot worse, learning how to walk than she ever did from falling off the bed. lol.