Eastern muck – I kept being sick (6)

I believe the answer is:

emesis

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

'eastern muck i kept' is the wordplay.
'eastern' becomes 'e'.
'muck' becomes 'mess' (I can't explain this - if you can you should give a lot more credence to this answer).
'kept' indicates putting letters inside.
'mess' enclosing 'i' is 'mesis'.
'e'+'mesis'='EMESIS'

'being' acts as a link.

Can you help me to learn more?

(Other definitions for emesis that I've seen before include "Throwing up" , "Technical name for vomiting" , "Vomiting; ie, mess (anag.)" , "sick" .)

I've seen this clue in The Guardian.

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