On the deja vu thing, I suffered from mild epilepsy for about four years. There is a very distinct deja vu at the onset of a seizure. At least for me. Was actually very enjoyable. I could never, and can't now, adequately describe it. Only that it was very strange and almost "other world". Never a druggie, so wasn't a flashback.
I worked at UPenn at the time so had the benefits of their extensive medical system. Lots of study, but never found a cause. Lasted for about 3-4 years and then went away without any medication or surgery. I always thought it was either from too much sex or not enough. Being a healthy person in my late 20's at the time, I worked on the 'not enough' thesis. Seems to have worked as I haven't had a problem in 25 years. Hope everyone else has the same good results.