I wake every morning with pretty bad stiffness in my neck and upper back and sometimes in the night too. I've always put it down to stress as I would get the same thing before my accident at times. I stress terribly over the thought of there being little bits of damage in my brain (thanks to all these theories about PCS) and the prospect of being permanently mentally unwell. If the problem is in your neck and you experience stiffness and fogginess, that sounds much more like stress/spinal issues than PCS (whatever PCS is!!).