‘坠入’ is a compound verb meaning 'to plunge into' — often describing a sudden, involuntary, or emotionally intense entry into a state (especially abstract ones like love, despair, confusion, or sleep). The first character 坠 (zhuì) means 'to fall' or 'to drop', evoking weight, gravity, and loss of control; the second character 入 (rù) means 'to enter'. Together, they emphasize not just entering, but doing so rapidly, deeply, and often uncontrollably — like falling headlong into water or darkness.

This phrase is commonly used in literary, descriptive, or emotionally charged contexts — especially in novels, songs, and formal speech. It rarely refers to physical entry into places (e.g., you wouldn’t say 坠入房间); instead, it’s reserved for intangible states: emotions (love, silence, chaos), conditions (sleep, unconsciousness), or metaphorical realms (illusion, memory, poverty). It carries a slightly poetic or dramatic tone and is seldom used in casual daily conversation.