Raise weapon over your head when half asleep (6)

I believe the answer is:

drowsy

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'half asleep' is the definition.
(I've seen this before)

I don't understand how the remainder of the clue works.

(Other definitions for drowsy that I've seen before include "Sleepy, lethargic" , "Wanting to nod off" , "Soporific" , "Being rather tired" , "Inclined to nod off" .)

I've seen this clue in The Irish Times.

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