Feel sick, having eaten fish (4)

I believe the answer is:

eels

I'm a little stuck... Click here to teach me more about this clue!

'eaten fish' is the definition.
'eels' can be an answer for 'fish' (I've seen this before). I'm not certain of the 'eaten' bit.

'feel sick having' is the wordplay.
'having' says the answer is hidden in the clue.
'EELS' can be found hidden inside 'feel sick'.

Can you help me to learn more?

(Other definitions for eels that I've seen before include "Long, fleshy fish" , "Conger --; jellied --" , "Slippery creatures" , "Sea creatures found in lees" , "eg Conger" .)

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.