The experience of thinking that something new has happened before (4,2)
I believe the answer is:
deja vu
'the experience of thinking that something new has happened before' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for deja vu that I've seen before include "Illusion of familiarity" , "Familiar feeling" , "Feeling of something having happened before" , "Eerie feeling of repetition" , "Already seen" .)