There have been multiple studies conducted under placebo controlled conditions.

This is a beautiful, new device that gives you detailed sleep tracking data, not just whether you're asleep or awake, but also your phase of sleep deep sleep, light sleep, REM sleep.

by A. P. Maudsley, 1928, repr.

References

All of the troops were able to hear the call of the shofar from their position because of its distinct sound.

Tom suffers from sleep apnea.

The REM sleep, rapid eye movement, dream state, is in light green and light is gray, light sleep and deep sleep, the best restorative sleep, is that dark green.

A night terror, sleep terror or pavor nocturnus is a parasomnia or sleep disorder, causing feelings of terror or dread, and typically occurs during the first hours of stage 3 4 non rapid eye movement (NREM) sleep.

I fought against sleep.

Sleep is necessary.

Sleep deprivation is extreme.

Sleep deprivation increases risk of heart attacks.

Monti, Jaime M., S. R. Pandi Perumal, Christopher M. Sinton (2008).

The noise disturbed my sleep.

The noise disturbed my sleep.

And we had sleep apnea at night.

OK. Now let's move from sleep to diseases.

Having less sleep than this is common among humans, even though sleep deprivation can have negative health effects.

And I learned the hard way, the value of sleep.

And I began the journey of rediscovering the value of sleep.

It can be caused by another disorder, by changes in the sleep environment, by the timing of sleep, severe depression, or by stress.

This is Sleep, the Virtual Choir.

Sleep is essential to health.

Aren't you sleepy?

Does the cough disturb your sleep?

Mary is talking in her sleep.

Mary wants to die in her sleep.

Tom became very sleepy.

Older people tend to sleep less overall but sleep in REM for about the same absolute time, and therefore spend a greater proportion of sleep in REM.

The course of the disease in animals is similar to the course of sleeping sickness in humans.

Are you sleepy?

I'm a light sleeper.

I'm not sleepy.

I'm sleepy.

I feel sleepy.

I'm a heavy sleeper.

Landlords aren't losing any sleep over these laws.

The poet compared death to sleep.

Don't lose sleep over that.

The baby seemed to be in a deep sleep.

Tom didn't seem to be asleep.

Are you sleepy or tired?

And this tells you, of course, how much you had in REM sleep, in deep sleep, and all this sort of thing.

There is now a kind of sleep deprivation one upmanship.

Sleep is the best medicine for a cold.