Grammar fix

deep sleep

restful sleep

A period of sleep when you are sleeping very well and your body and mind fully rest, usually without waking up easily.

collocationB1common

Hear it in context

Notice where the phrase sounds natural.

After a long day, I fell into a deep sleep and didn’t wake up until morning.daily life
Getting enough deep sleep is important for your health because it helps your body recover and your mind feel clear the next day.IELTS speaking

Pattern: in deep sleep; fall into deep sleep; be in a deep sleep

WrongI was in deep sleep when you called.

RightI was in a deep sleep when you called.

'In A deep sleep' needs the article.

Patternin deep sleep; fall into deep sleep; be in a deep sleep

Choose the version that sounds natural in speech.

Stiff I was in a state of profound slumber.

Natural I was in a deep sleep.

'Profound slumber' is literary; 'in a deep sleep' / 'fast asleep' is natural.

Words that usually travel with it.

'Light sleep' means you wake up easily; 'deep sleep' means you are hard to wake.