Translation guide
In Japanese, expressing 'deep sleep' involves describing the quality or depth of sleep rather than using a single direct equivalent. The most common and natural ways range from casual phrases about sleeping soundly to more formal or technical terms for deep sleep stages.
To say someone is in a deep sleep or slept deeply, often implying they were hard to wake.
The most common and natural way to say 'sleep deeply' or 'sleep soundly'. ぐっすり is an onomatopoeic adverb meaning 'soundly'.
昨夜はぐっすり寝た。
I slept deeply last night.
I was sleeping so deeply that I didn't notice the earthquake.
A slightly more formal or written term meaning 'deep sleep' or 'sound sleep'. Often used in contexts like 'I got a good night's sleep'.
熟睡して疲れが取れた。
I slept deeply and recovered from fatigue.
Literally 'fall into a deep sleep'. A more literary or descriptive expression, often used in narratives.
彼は深い眠りについた。
He fell into a deep sleep.
Slang term meaning 'sleeping like a log' or 'crashing out'. Very casual and vivid.
昨日は爆睡した。
I crashed out yesterday.
Referring to the physiological stage of deep sleep, such as slow-wave sleep.
The direct translation used in medical or scientific contexts to refer to deep sleep stages.
深い睡眠は体の回復に重要です。
Deep sleep is important for physical recovery.
The technical term for 'slow-wave sleep', a specific stage of deep sleep. Used in medical or scientific literature.
徐波睡眠はノンレム睡眠の一部です。
Slow-wave sleep is a part of non-REM sleep.
Describing someone who is in such a deep sleep that they are difficult to rouse.
Describes a state where one's sleep is deep, often implying they are hard to wake. Can be used as a general characteristic.
彼は眠りが深くて、なかなか起きない。
He is a deep sleeper and doesn't wake up easily.
Emphasizes being completely in a deep sleep, often to the point of being unaware of surroundings.
ぐっすり寝込んでいて、電話に気づかなかった。
I was in such a deep sleep that I didn't notice the phone.
ぐっすり寝る is the everyday expression for sleeping soundly. 熟睡する is more formal and often used in writing or when emphasizing the quality of sleep. In casual conversation, ぐっすり is preferred.
Directly translating 'deep sleep' as 深い睡眠 in everyday conversation sounds unnatural. Use ぐっすり寝る or 熟睡する instead. 深い睡眠 is mainly for technical contexts.