Doctor emails about a debility (7)
I believe the answer is:
malaise
'debility' is the definition.
(thesaurus)
'doctor emails about a' is the wordplay.
'doctor' indicates anagramming the letters.
'about' indicates putting letters inside.
'emails' with letters rearranged gives 'mlaise'.
'mlaise' going around 'a' is 'MALAISE'.
(Other definitions for malaise that I've seen before include "General feeling of discomfort" , "Uneasy feeling" , "Feeling of impending illness" , "sickness" , "Feeling of illness or mental uneasiness" .)