Trouble with nerve — in bed this may help (3-5,6)
I believe the answer is:
hot-water bottle
'in bed this may help' is the definition.
(a hot-water bottle might be used in bed)
'trouble with nerve' is the wordplay.
'trouble' becomes 'hotwater' (I've seen this before).
'with' says to put letters next to each other.
'nerve' becomes 'bottle' (I've seen this before).
'hotwater'+'bottle'='HOT-WATER BOTTLE'
(Other definitions for hot-water bottle that I've seen before include "night heater" , "Bed warmer" , "comfort in retirement!" .)