expression, adverb
without sparing time for sleep; sacrificing sleep
Fixed adverbial phrase used when someone works or does something so intently that they begrudge even the time for sleeping.
彼は寝る間も惜しんで勉強した。
He studied without sparing time for sleep.
寝る間も惜しんで働いた結果、体を壊してしまった。
As a result of working without sparing time for sleep, he ruined his health.