Uneasy about an overwrought Sioux (7)
I believe the answer is:
anxious
'uneasy' is the definition.
(similar in meaning)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for anxious that I've seen before include "Jittery" , "Fretful, worried" , "Uneasy, worried" , "Nervy" , "Apprehensive, uneasy" .)