Go back as doctors do when illnesses recur (7)
I believe the answer is:
retreat
'go back' is the definition.
(to retreat is to withdraw or go back)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for retreat that I've seen before include "secluded place" , "Tree rat (anag)" , "Give ground" , "Pull back" , "It may be secluded" .)