to doze, to nap, to nod
盹 centers on a brief, involuntary loss of wakefulness: dozing off, napping lightly, or nodding with sleep. The meanings all describe a short, light sleep or the act of drifting off.
盹 combines 目 (eye) with 屯, which likely contributes the sound. The character suggests an eye-related action, fitting the meanings of dozing or nodding off where the eyes close briefly.
The eye 目 on the left is paired with 屯, which looks like a sprout struggling to push through. Imagine your eyes struggling to stay open, finally giving in to a nap.
For シュン, picture someone dozing off and then suddenly waking with a 'shun' sound, like a quick, sharp intake of breath. The 'shun' sound cues シュン, and the sudden awakening fits the brief nap.