Initially dismiss everything just as very unusual and weird sensation (4,2)
I believe the answer is:
deja vu
'weird sensation' is the definition.
(unusual sensation in the mind)
'initially dismiss everything just as very unusual' is the wordplay.
'initially' suggests taking the first letters.
The first letters of 'dismiss everything just as very unusual' is 'DEJA VU'.
'and' is the link.
(Other definitions for deja vu that I've seen before include "Feeling of something having happened before" , "The experience of thinking that something new has happened before" , "Sense of history repeating" , "strange experience?" , "Feeling one has seen a thing before" .)