Mad to fall off a chair (3,4,6)
I believe the answer is:
off ones rocker
'mad to fall' is the definition.
I know nothing about this answer so I cannot tell whether this works.
'off a chair' is the wordplay.
I cannot really understand how this works, but
an anagram of 'off' is 'ffo' which is within the answer.
'a' could be 'one' and 'one' is found within the answer.
'chair' could be 'rocker' (rocker is a kind of chair) and 'rocker' is found within the answer.
A single letter 's' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for off ones rocker that I've seen before include "How a seated person might fall" , "not favouring my dove, > like a fallen Ronnie C?" , "Insane" , "Crazy, totally mad" .)