Fizzy drink is what a hypochondriac might have, we hear (9)
I believe the answer is:
champagne
'fizzy drink' is the definition.
(I've seen this before)
'what a hypochondriac might have we hear' is the wordplay.
I cannot really see how this works, but
'a' could be 'amp' (A is the symbol for the amp or ampere) and 'amp' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'is' acts as a link.
Can you help me to learn more?
(Other definitions for champagne that I've seen before include "toast can be made with it" , "region of France" , "The drink called bubbly" , "French 'sparkler'" , "Sparking drink" .)