You've piqued my curiosity now.

The other possibility that jumps out to me is epilepsy. Have you had an EEG done, to rule out any abnormal brain activity?

I, myself, have epilepsy. DID is automatically ruled out for people who have epilepsy. So, while I frequently suffer dissociation and depersonalization, DID is an inaccurate diagnosis for me. Doctors presume that I am experiencing auras (also known as simple partial seizures) when they occur.

If you are experiencing the sensation rather often, and don't feel that stress is a likely candidate, then looking at your brain (physiologically) would be an important step in discovering and physical cause for the experience.

My epilepsy was mis-diagnosed as an anxiety disorder when I was around 21 y.o. My auras often involved intense deja vu, as well as the depersonalization, and occurred at all kinds of times and places. It took several years of panic disorder treatment before the abnormal brain activity secondarily-generalized and became tonic-clonic (aka ~ "grand mal"). And that is when treatment really began for me.

As a result, I highly recommend looking into all possibile diagnoses. The sooner you find the cause, the better the outcome. Trust me on that!

Very best wishes to you!