Sleep is a major part of health and well-being — and a big part of our lives as well. We spend a third of our lives in a state of sleep. But our modern understanding of sleep was developed only in the last century, when scientists became intrigued by the eye movements they saw in sleeping infants. Until that time, most people didn't realize the vital role that sleep plays in our health and well-being, including the way sleep actually helps improve your mental and emotional function and even has a role in the formation of memories.

Research revealed that sleep actually occurred in five distinct stages, which are divided into REM (rapid eye movement) sleep and NREM (non-rapid eye movement) sleep. NREM, the first part of the sleep cycle, breaks down into four stages that can be measured by the electrical waves seen on an electroencephalogram (EEG) machine.

In stage one, you transition from being awake to being asleep. You gradually lose awareness of your surroundings, and your breathing begins to slow. As you progress from stage one to stage two, your sleep deepens. Together, stages one and two are known as alpha sleep, named for the waves seen on an EEG.

In stages three and four, you experience your most restorative sleep. The brain waves in this stage, called delta waves, are very slow. In these stages, you are immersed in your deepest phases of sleep and least likely to be awakened. Your heartbeat and breathing become very slow and regular, and your body achieves a state of deep relaxation. It is during these two final stages that your body secretes important immune-boosting substances and growth hormone, a substance for repairing muscles. Without these two stages of sleep, you do not awaken feeling refreshed.

Throughout the night, you move gradually from each level of sleep to the next, without ever skipping over a phase. Interestingly, it's only from stage one that you move into REM sleep, the stage of sleep in which dreams occur. In REM, your brain is also undergoing the process of storing long-term memory. Some people even notice that they experience a dreamlike state as they're falling asleep. Though most people reach REM sleep ninety minutes after they first fall asleep, the bulk of REM sleep occurs toward the end of a night's rest. The five stages of sleep continue to cycle throughout the night, with the sleeper spending a total of sixty to ninety minutes in each stage. During a typical night, a healthy person will repeat each cycle several times a night.

Now that you have fibromyalgia, sound sleep might seem like an entirely foreign concept. Whether it's the pain that causes sleep disturbance, or the sleep disturbance that is causing the pain remains uncertain. But as many as 90 percent of all people with fibromyalgia report having sleep problems.