Baby's and Toddlers are top heavy, their heads outweigh the rest of their body. So falls and bumps are normal. I have worried so much about this same topic in the past. This is the main reason I always keep the bathroom doors shut with door knob protectors on them. Kids can drown in the water, they tip over and can't get their heads out due to the weight of the head and lack of strength of their neck and back muscles.
After Natasha Richardson died from the fall where she bumped her head I was frantic. She was physically gone just a few hours later, there wasn't really anything that could have been done. If she had been checked by a doc right away who knows, maybe she'd still be alive.
I called the pediatrician and visited with the nurse. Then when we had our next well child appointment I got a list of good things to watch for.
Also, I googled this topic and here are some good links to read about this:
The google page:
http://www.google.com/search?sourceid=chrome&ie=UTF-8...
Dr. Sears tells what to look for:
http://www.askdrsears.com/topics/childhood-illnesses/head...
Kids health organization:
http://kidshealth.org/parent/firstaid_safe/emergencies/he...
Baby center details:
http://www.babycenter.com/0_falls_11249.bc