So just to be clear, the internal weird feeling as if my brain slams into the skull is just an illusion of some sort? To describe it, it's in a way the same tingling feeling I got from fast side to side movement, now it's just coming from up and down movement instead. An earlier comment of yours in this thread just seem to mention that repetitive forward and backward movement of the head seemed to cause cumulative trauma and so this worries me since I believe it then poses a greater risk of injury than that of turning the head side to side. So the weird sensation you get for example from nodding your head fast is harmless? If it's even normal to feel what I'm talking about? Can it be the body's sensory defense system warning me to slow down before it actually causes any damage or something? Even when I'm nodding, all it takes is doing it a bit fast with followed by a sudden stop and then for a very short duration of time, I can feel some sort of internal pressure, hopefully just because it's provoking blood circulation. I also just kinda wanna know if you most likely would pass out from shaking your head before trauma occurs? Or would your neck get severely damaged? To summarize, I'm hoping that the answer is the body's natural response activating some cautionary mechanism and not actually movement of the brain I can feel either inside or outside my head, can't tell.