Lay awake initially beset by terrible ulcers (7)
I believe the answer is:
secular
'lay' is the definition.
('secular' can be a synonym of 'lay')
'awake initially beset by terrible ulcers' is the wordplay.
'initially' indicates taking the first letters.
'beset by' is an insertion indicator ('beset' could historically mean 'cover').
'terrible' indicates an anagram.
The initial letter of 'awake' is 'a'.
'ulcers' with letters rearranged gives 'seculr'.
'a' placed into 'seculr' is 'SECULAR'.
(Other definitions for secular that I've seen before include "Not religious or sacred" , "Not connected with religion" , "Lay" , "Worldly" , "Concerning the laity" .)