deja vu

In our book it says that 2/3rds of all people have some sort of deja vu sometime in their lives. I don't know about other people but i have it a lot, maybe a couple times a month. The last time it happened was the other day and i was really tired and stressed and the book mentions that being stressed and over tired could affect deja vu. My deja vu's also are never really of something that is going on (example being someone walking passed me) but mine are just of people saying things in a conversation to me. i want to keep track of how I'm doing physically whenever this happens and see if being tired or stress really does affect my deja vu. If you know what affects yours i would be interested in knowing.