I've been trying to figure out the same thing as well. I was doing well a year and 4 months after the original injury. No headaches or symptoms (except tinnitus) unless I jar my head or shake it a little bit, then the relapses come. Recently I got one from taking a CPR training course. Apparently doing chest compression for a minute and a half is too much for my head. Gave me the worst PCS I've had in 6 months. It's been 2 weeks and I still don't feel right.