Or not! I write and ride reasonably competently having had two head fractures - one as a baby when I fell out of a tin bath on a table onto the floor and the second as a kid falling off a wall. My skull is now an interesting shape if you would like a quick feelThe thing about a serious head or hip injury is that you could write about it on a forum afterwards when breaking a hip, but get a serious head injury, and you may never have that option again...even if you live.
Head injuries can be serious - or not. Skulls and contents can withstand great damage and deformation. Or you can just be unlucky and a small bump (with/without helmet) may lead to life changing or terminating trauma. This issue is compounded by the fact that superficial cuts usually generate great outpourings of blood because of the way our circulations work. This can make many head injuries look a great deal worse than they really are.