Trapped on the snowy mountain, his life hung by a thread.
Tips
history
From the Tang-dynasty letter 《为建安王与诸将书》 by Chen Zi'ang (陈子昂), describing soldiers who "all suffered edema, with their lives hanging between dawn and dusk." 旦夕 (dànxī) literally means "morning and evening" — the span of a single day.
usage
Used for serious medical or peril situations only. Not a casual exaggeration. Synonym: 危在旦夕 (wēi zài dànxī, danger in dawn and dusk).