Feel poorly when caught by right cross, something doctor may check (6)
I believe the answer is:
reflex
'cross something doctor may check' is the definition.
I can't judge whether this definition defines the answer.
'feel poorly when caught by right' is the wordplay.
'poorly' indicates an anagram (a poor spelling).
'when' becomes 'x' (I am not sure about this - if you are sure you should believe this answer much more).
'caught by' means one lot of letters goes inside another.
'right' becomes 'r' (abbreviation).
'feel' anagrammed gives '[feel]'.
'[feel]'+'x'='eflex'
'eflex' placed around 'r' is 'REFLEX'.
Can you help me to learn more?
(Other definitions for reflex that I've seen before include "Bent backwards" , "Automatic instinctive reaction" , "Unthinking response" , "Movement in response to a stimulus" , "Action not requiring conscious thought" .)