Lots of people get this "jamais vu" symptom. Mine came on out of nowhere last year, even though i had already had DP/DR for a few years already. For some people it is just caused by DP/DR itself, but I got mine checked out and found out from a neurologist that it was due to a milder form of epilepsy (complex partial seizures) that I didn't know I had and this symtom of things looking unfamiliar has gone away ever since I started meds for epilepsy.