It's so scary when they fall, isn't it? My then-22-month-old took a tumble down our steep wooden deck stairs and hit his forehead on a paving stone below. Left a nice big goose egg and a very colorful bruise and freaked me out for about two days. I kept him awake for a few hours, even though (of course) it happened right before his nap time, and then sort of checked on him intermittently through the night to make sure he was okay. That was weeks ago and he's totally fine now.
Without any symptoms of serious head injury (loss of consciousness, disorientation, pupils asymmetrical or not tracking simultaneously, vomiting immediately after fall, fluid leaking from nose and/or ears, etc.) there's probably no reason to worry.
You might consider also getting a copy of How to Raise a Healthy Child in Spite of Your Doctor
by Robert Mendelsohn, M.D. and Take Charge of Your Child's Health: A Parents' Guide to Recognizing Symptoms and Treating Minor Illnesses at Home
by George Wootan, M.D. Both have an excellent section on head injuries and have reassured me many times over the last couple of years.