Sleep on it (10)
'sleep on it' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cot that I've seen before include "Small child's bed" , "baby carrier?" , "Small boat to hold a baby" , "Infant's bed" , "Crib" .)
(Other definitions for pillowcase that I've seen before include "Item of bed linen" , "Item of bedlinen" .)