Get down for a sleep (3)
I believe the answer is:
nap
'a sleep' is the definition.
(a nap is a short sleep)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for nap that I've seen before include "A brief snooze" , "Raised fibres on surface of cloth or leather" , "Kip" , "Little sleep" , "A daytime doze" .)