At home, confined to bed, rejected pick-me-up (5)
I believe the answer is:
tonic
'pick-me-up' is the definition.
(I've seen this in another clue)
'at home confined to bed rejected' is the wordplay.
'at home' becomes 'in' ('I'm in' can mean 'I'm at home').
'confined to' indicates putting letters inside.
'bed' becomes 'cot' (cot is a type of bed).
'rejected' is a reversal indicator.
'in' inserted into 'cot' is 'cinot'.
'cinot' reversed gives 'TONIC'.
(Other definitions for tonic that I've seen before include "Important note" , "something nice and fresh" , "do for musicians" , "A pick-me-up drink, nice with gin" , "Invigorating liquid" .)