Dread man losing his head during film (5)
I believe the answer is:
panic
'dread' is the definition.
(panicking is a kind of dreading)
'man losing his head during film' is the wordplay.
'losing his head' means to remove the first letter.
'during' means one lot of letters goes inside another.
'film' becomes 'pic' (I've seen this in other clues).
'man' with its initial letter taken off is 'an'.
'an' going inside 'pic' is 'PANIC'.
(Other definitions for panic that I've seen before include "Overwhelming feeling of fear and anxiety" , "Lose one's cool" , "general alarm" , "Overwhelming terror" , "Frantic fright" .)