The zzz on a sleepy kaomoji like ( ˘ω˘ )zzz comes from comics, where snoring was drawn as 'zzz'. Kaomoji borrowed it — more z's, the deeper the sleep.

A 🌙 or ☽ beside a face — ( ᵕᴗᵕ )🌙 — sets the night scene instantly. It turns any calm face into a good-night.

In (－ω－) and ( ˘ω˘ ) the eyes are half-closed lines — that heavy-lidded, about-to-doze look. The flatter the eyes, the sleepier.

Japanese end the day with おやすみ (oyasumi), 'rest well.' Night kaomoji carry that gentle warmth — soft and cozy, made to send before bed.

The 旦 or 🍵 in (´ω`🍵) is a warm drink before sleep. Pair it with zzz and it's the wind-down-and-doze-off moment in one line.