Took beauty treatment lying down (5)

I believe the answer is:

slept

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'took' is the definition.
The answer and definition can be both related to bodily activities as well as being past participle verbs.
Maybe there's an association between them I don't understand?

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for slept that I've seen before include "Napped, dozed" , "Snoozed" , "Had forty winks" , "Was dormant" , "Had room for" .)

I've seen this clue in the Evening Standard.

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