abhava pratyaya alambana tamo vrttir nidra
अभावप्रत्ययाअलम्बना तमोवृत्तिर्निद्र

Deep sleep is the non-existent impression rooted in still thoughts

Yoga Sutras of Patanjali, 1.10

nidra = sleep

abhava = non-existent
pratyaya = impression
alambana = based (on)
tamo (tamas) = void, inertia, darkness
vrttir = thought

I love sleeping people – they look so calm and at peace.
The translations I read described this as being about deep, dreamless sleep.
It’s interesting that it gets included as a “thought”. I find sleep fascinating – it’s almost as mysterious as infinity and thinking about the edge of the cosmos.