Lack of action in vampires is at sunrise, on reflection (6)
I believe the answer is:
stasis
'lack of action' is the definition.
(I've seen this before)
'in vampires is at sunrise on reflection' is the wordplay.
'in' indicates the answer is hidden within the clue.
'on reflection' says the letters should be written backwards.
'sisats' is hidden in the letters of 'vampires is at sunrise'.
'sisats' backwards is 'STASIS'.
(Other definitions for stasis that I've seen before include "Stoppage of blood flow in body" , "Secret police force's" , "lack of action" , "Inactive state" , "Assist with stagnant condition" .)