Bath possibly an afterthought when getting up (3)
I believe the answer is:
spa
'bath' is the definition.
(I've seen this before)
'an afterthought when getting up' is the wordplay.
'an' becomes 'a'.
'afterthought' becomes 'ps' (ps stands for postscript).
'when getting up' is a reversal indicator.
'a'+'ps'='aps'
'aps' backwards is 'SPA'.
'possibly' acts as a link.
(Other definitions for spa that I've seen before include "Where people go for spring" , "here for healthy holiday" , "Bath - mineral water spring" , "hydro" , "A curative mineral spring, or place with one" .)