Mark, do you think the hardness of the colliding object also makes a difference to the Gs apart from speed ? For instance, I hit my head on a cement wall and not table with roughly same speed of 2m/s. What do you think G would be in my case ?

Also one thing I don't understand. Technicality, if the brain bounces back and forth after a concussion , then how do lower forces make it bounce back and forth after a single concussion ? For example let's assume a person has had a concussion with a 40G force which let's assume is enough to bounce a brain back and forth. Now this person has had a few more concussions after that and his brain is super sensitive yo even lower G forces. Does that mean now even with 10G force his brain will bounce back and forth ? This sounds crazy to me. Or is it some chemical balance that is disrupted more easily with each successive concussion and not necessarily bouncing back and forth phenomenon?