Hi all! I just saw this thread and though this doesn't sound like everybody in this thread's situation I just wanted to bring it to attention! I had very bad exercise intolerance after my concussion and my symptoms were taking a lot longer to diminish than we felt they should. I also started passing out after standing for too long so we knew something else was going on besides just a concussion. We found out that I have POTS (postural orthostatic tachycardia syndrome) which isn't a very well known condition which is why I was not diagnosed sooner. They are not sure what causes POTS but it often follows a concussion so it is lead to believe concussions may cause it! It is a disfunction of the autonomic nervous system and it causes a vast amount of symptoms such as head aches, brain fog, dizziness (things that are also concussion symptoms) but it's main symptom is exercise intolerance. It's worth looking into because once I began being treated for the POTS more than half of my symptoms diminished and my main focus is now on treating my POTS. Hope you all start to feel better! Definitely look into POTS!