Mental dullness leads to much faulty posture (6)

I believe the answer is:

stupor

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'mental dullness' is the definition.
'stupor' can be an answer for 'dullness' (thesaurus). I am not certain of the 'mental' bit.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for stupor that I've seen before include "State of near unconsciousness" , "Almost unconscious condition caused by drink or drugs" , "Coma - lassitude" , "Daze or torpor" , "Dazed state; Proust (anag.)" .)

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