Sleep restlessly (4)
I believe the answer is:
toss
'sleep restlessly' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for toss that I've seen before include "Ditch" , "Throw carelessly" , "Raise a bit of money before opening" , "Do it with caber in Scotland" , "have a restless night, perhaps" .)