Rested up before dawn of day, stunned (7)
I believe the answer is:
tasered
'stunned' is the definition.
(I've seen this before)
'rested up before dawn of day' is the wordplay.
'rested' becomes 'sat' (to sit is to rest).
'up' is a reversal indicator (in down clue: letters go upwards).
'before' becomes 'ere' (poetic term).
'dawn of' suggests taking the first letters.
The initial letter of 'day' is 'd'.
'sat' backwards is 'tas'.
'tas'+'ere'+'d'='TASERED'
(Other definitions for tasered that I've seen before include "Dearest (anag.)" , "stunned by shock" , "Immobilised by electrified darts" .)