Good health - it's not something you often see in hospital! (8)
I believe the answer is:
sickness
'good health' is the definition.
'sickness' can be an answer for 'health' (I have seen 'Ill health' mean 'sickness' so perhaps 'health' could also mean 'sickness'). I am not certain of the 'good' bit.
'it's not something you often see in hospital' is the wordplay.
I cannot really understand how this works, but
'it's' could be 'es' ('e' can mean 'electronic' which is similar to 'IT') and 'es' is found in the answer.
'see' could be 'c' (the word for the letter, according to Chambers) and 'c' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sickness that I've seen before include "Illness, disease" , "Illness, malady" , "It's not looking good" , "Infirmity" , "State of being ill" .)