This is the one symptom whose cause remains elusive to me. I've spent a lot of time thinking about possible mechanisms. I always seem to come back to the notion that there must be an acquired maladaptive response to handling rising intracranial pressure (such as the case with a valsalva manoeuver) in some people after a mTBI or that there is a heightened sensitivity to ICP even in the physiologic ranges. The other questions is whether the problem stems from the arterial or venous side of the cerebral vascular system, or both.

I have been trying to figure things out from the venous side given that the pressure is definitely related to straining. One of the things I'm trying to figure out is the adaptive response in a "normal" brain when someone in turned upside down for a prolonged period of time. In this situation, cerebral venous hydrostatic pressure rises quickly which must drive fluid out of the vessel and into the interstitial space of the brain. How does the brain cope with this fluid shift on the short term such that homeostasis is maintained? What leads to this homeostatic mechanism to eventually falter over time if the upside down position isn't eventually corrected? Perhaps there is similarity is what occurs after an mTBI. Just wondering out loud.
Anyone with theories?