Rumbles terribly in one's sleep! (7)

I believe the answer is:

slumber

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

'one's sleep' is the definition.
'slumber' can be an answer for 'sleep' (synonyms). I am not sure about the 'one's' bit.

'rumbles terribly' is the wordplay.
'terribly' is an anagram indicator.
'rumbles' is an anagram of 'SLUMBER'.

'in' is the link.

Can you help me to learn more?

(Other definitions for slumber that I've seen before include "Snooze" , "Drop off" , "Sleep" , "nap" , "Overnight social event for (American) teenage girls" .)

I've seen this clue in the Evening Standard.

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