Sometimes it feels like what is accruing at the present time is attached to something else, every time you hear or smell something or see something accruing reminds you the situation that you have been or experienced longtime ago, so what do you call it?
A flashback: (from TFD)
- a vivid memory that arises spontaneously or is provoked by an experience.
an experience that has characteristics of an earlier experience.
- She added, "I was worried sick when Howie came out here, like maybe he'd get a flashback of us together and be in love with me or something stupid."
or a deja vu;
An impression of having seen or experienced something before:
- Old-timers watched the stock-market crash with a distinct sense of deja vu.
For "urelated situations, I'd go for "an (false) association"