Rule of thumb for falls - take their height, if they fall from anything higher than that, it's potential for more severe injuries (break and things). If they fall from their height or less it's just like tripping and falling, the body is designed to absorb falls from those heights. My LO fell off our bed rolling around in her sleep around 14 or 15mos, slid head first between bed and wall, quick cry and right back to sleep. I knew she was fine although it certainly woke me up. Our bed is fairly high but she was just about even with it so I didn't worry because I know my kiddo...and having a DH who's an EMT and having done the class myself I can do a quick head to toe check if need be. Now I know someone who left their 9mo alone on the changing table (well, the 4yo was in charge of watching her...) and she broke her clavicle when she hit the ground but no concussion. Like PP mentioned, concussions, at least those that would warrant a doctors visit, are pretty apparent. I've had a few mild ones and one nasty one with minor blackout and they feel very different and are easy to pick out by the behaviors.
An egg on the head is not the worst thing to have, it's a sign of trauma to that area, bruises indicate broken blood vessels in the skin and the swelling is an inflammatory response of blood and fluids rushing to the area to heal it. DD's bed plunge was nothing compared to when she face-planted on her elephant ball blowing toy as she was beginning to walk - nice black eye, massive egg on her forehead over one eye, but after a 30 second cry she began to scold the toy which told me in spite of how horrible it looked, she was just fine! That and a black in the ER on a 9mo would warrant an immediate DCF investigating frenzy around here which I was just not interested in dealing with.