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.

Tom suffers from sleep apnea.

Sleep deprivation is extreme.

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

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.

I like winter.

I don't like winter.

Do you like winter?

Do you like winter?

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.

Are you sleepy?

I'm a light sleeper.

I'm not sleepy.

I'm sleepy.

I feel sleepy.

I'm a heavy sleeper.

References

I like the smell of winter.

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.

Tom doesn't like winter.

There is now a kind of sleep deprivation one upmanship.

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.

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

And sleep disorders.

Are you sleepy?

Aren't you sleepy?

Aren't you sleepy?

Aren't you sleepy?

I'm still sleepy.

I fought against sleep.

I was sleepy.

I'm not asleep, meh.

You're sleepy.

You're sleepy.

Tom is sleepy.

We're sleepy.

I'm getting sleepy.

Tom was sleepy.

Sleep is necessary.

Everyone's sleepy.

I didn't feel sleepy.