This might be the psychological state of doctor who had Omicron twice. (4)

I believe the answer is:

mood

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'state of doctor who had omicron twice' is the definition.
'mood' can be an answer for 'state' (mood is a kind of state). I'm unsure of the rest of the definition.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for mood that I've seen before include "Disposition" , "Bad feeling" , "at times appears very high" , "Frame of mind" , "Doom (anag)" .)

I've seen this clue in The Irish Times.

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