Beginning to go mad, upset and hurt (5)
I believe the answer is:
stung
'hurt' is the definition.
(sting can mean to hurt)
'beginning to go mad upset' is the wordplay.
'beginning to' indicates taking the first letters.
'mad' becomes 'nuts' (I've seen this before).
'upset' says the letters should be written in reverse.
The initial letter of 'go' is 'g'.
'g'+'nuts'='gnuts'
'gnuts' written backwards gives 'STUNG'.
'and' acts as a link.
(Other definitions for stung that I've seen before include "Offended" , "Wounded by, eg, bee" , "piqued" , "Caused sharp pain" , "Aroused to impatience or anger" .)