Sleep poorly (4,3,4)
'sleep' is the definition.
(to doss is to sleep in an improvised bed)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for doss that I've seen before include "going off to sleep" , "go to bed" , "Sleep like a tramp" , "Sleep (in cheap lodgings?)" , "Sleep somewhere convenient" .)
(Other definitions for toss and turn that I've seen before include "count sheep" , "Be wakeful and fidgety" , "Be restless (in bed)" , "Be unable to sleep" , "rest uneasily" .)