Tense, suffering from a hangover in the morning? (7)
I believe the answer is:
uptight
'tense' is the definition.
(similar in meaning)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for uptight that I've seen before include "Unable to express one's feelings" , "Ill at ease" , "Tense, nervous, repressed" , "nervy state" , "Tense - cross" .)