अभावप्रत्ययालम्बना तमोवृत्तिर्निद्र ॥१०॥
abhāva-pratyaya-ālambanā tamo-vṛttir-nidra ||10||

[RS] 1.10 Deep sleep is the absence of all impressions resulting from opacity in that which is mutable in human beings (chitta).

[JW] 1.10 Sleep is a fluctuation of [mind-stuff] supported by the cause (pratyaya, that is tamas) of the [transient] negation [of the waking and the dreaming fluctuations].

[SS] 1.10 That mental modification supported by cognition of nothingness is sleep. [p17]

[TD] 1.10 Deep sleep is when the mind is over come and heaviness and no other activities are present. [p152]

[EB] 1.10 Deep sleep is that state of mind which is based on an absence [of any content]. [p41]

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(अभाव, abhāva) = absence; non-presence; lack
(प्रत्यय, pratyaya) = impressions; that which is in the mind; opacity of chitta, i.e. impressions in chitta via vrittis.
(आलम्बन, ālambana) = support, basis, interrelationship, based on
(तमो, tamo) = inertia. Tamas is one of the three gunas, i.e. the basic properties of matter.
(वृत्ति, vṛtti) = lack of clarity; waves; thought waves
(निद्रा, nidrā) = sleep; deep sleep