I get exactly the same! Everything you described I understand completely. I have had an eeg as I thought it could be simple partial seizures but my eeg was clear, however, I unfortunately did not experience one of these episodes whilst having the eeg though I was very much derealized! Have you looked into the possibility that this could be a variant of migraine? Do you feel off balance and dizzy at times? Do you get any other symptoms along with the brief episodes of jamais vu? All this started for me after I got an ocular migraine aura which caused a massive panic attack and derealization started from there. Do you have any light sensitivity? Do lights am much brighter than before? If so this could be a persistent migraine aura that you are experiencing. Would love to hear your reply. Jen