Fancies a doctor must have the same trouble (6)
I believe the answer is:
dreams
'fancies' is the definition.
(I've seen this before)
'a doctor must have the same trouble' is the wordplay.
'a doctor' becomes 'Dr' (abbreviation).
'must have' says to put letters next to each other.
'trouble' is an anagram indicator.
'same' with letters rearranged gives 'eams'.
'dr'+'eams'='DREAMS'
(Other definitions for dreams that I've seen before include "Fancies" , "'We are such stuff / As dreams are made on' (The Tempest)" , "Fantasies; fantasises" , "Thoughts and visions during sleep" , "'''We are such stuff as ... are made on'' The Tempest (6)'" .)