Staggered because heavy weight I dropped (10)
I believe the answer is:
astonished
'staggered' is the definition.
(I've seen this before)
'because heavy weight i dropped' is the wordplay.
'because' becomes 'as' (I've seen this in other clues).
'heavy weight' becomes 'ton' (I've seen this before).
'dropped' becomes 'shed' (shedding is a kind of dropping).
'as'+'ton'+'i'+'shed'='ASTONISHED'
(Other definitions for astonished that I've seen before include "lost for words" , "dumbfounded" , "Sad one, this (anag)" , "Full of amazement" , "Amazed" .)