One possible cause of DPDR that is altered hormone levels after a concussion due to damage to the HPA axis. There is a video of a guy who cured his DPDR after a year of testosterone replacement therapy on Youtube. I cannot post links but it will show up with a search of "dpdr and hormones" on Youtube.

I am clinging on to the hope that this is the cause of mine, not seizures, because it is truly debilitating.