The quality of sleep is just as important as the quantity.

There are four major reasons one might sleep poorly:

1. Too little sleep.
2. Too many interruptions of sleep.
3. Abnormal sleep architecture.
4. Reasons not understood by medical science.

Too many interruptions of sleep

For reasons unknown, the brain needs long periods of uninterrupted sleep.

Suppose one night your telephone rang every minute and woke you up for 12 seconds each time. Suppose also this went on for 10 hours. Even though your brain would spend 8 of the 10 hours asleep, you would certainly awaken in the morning and say you slept poorly.

The problem is, of course, you did not get enough uninterrupted sleep. But do not get the idea that uninterrupted sleep normally lasts for hours.

Depending on age, the sleeping adult brain normally awakens about 15 times per hour.  For children, it's 8 to 9 times per hour.  Amazingly, we don't remember these normal awakenings in the morning, probably because they are brief.

A disease such as sleep apnea can greatly increase the number of awakenings, to more than 100 per hour in severe cases. And none of these awakenings may be remembered in the morning! (This is what makes sleep apnea so difficult to diagnose.)

Some persons with sleep apnea complain about their sleep quality. Others do not. In some cases without complaints, the decrease in sleep quality comes on so slowly that the person cannot remember what a good night's sleep was like. In other such cases, the person seems immune to an effect of frequent awakenings on sleep quality, for reasons not understood.

Because poor sleep quality can result from a serious condition (sleep apnea), it is a symptom that physicians should hear about.

Classically, there are five stages of sleep: stages 1, 2, 3, 4, and REM (rapid eye movement).

Of these, stage 4 sleep is the most restful. So, all other factors being equal, a person getting less stage 4 sleep will feel less rested than a person with more stage 4 sleep. (But it would be abnormal to have 100% stage 4 sleep in a night.)

Normally, all the sleep stages occur each night, and they occur in a pattern that is defined as "normal." This normal pattern may be disrupted, however:

• Alcohol, certain medications, and certain diseases (e.g. narcolepsy) can alter the pattern.
• Sleep apnea typically reduces the amount of stage 3, stage 4, and REM sleep, sometimes eliminating them.

Thus, there are multiple reasons why sleep apnea may decrease sleep quality.

As we have seen, apneas (and other types of breathing events) can repeatedly awaken the brain, alter sleep architecture, and reduce sleep quality.

However, sleep quality may also be reduced by breathing events that do not awaken the brain.

The nature of these breathing events, and the nature of the sleep disturbances, are not completely known. In many cases, however, snoring is an important feature.

A lesson to draw is: Snoring may be an indicator of poor sleep due to breathing problems, even when so-called "gold standard" tests (such as the polysomnogram) are normal. In such situations, a therapeutic trial may be warranted.