Disorder that affects the brain’s ability to control the sleep-wake cycle.

The disorder that affects the brain's ability to control the sleep-wake cycle is known as Narcolepsy. Here are the steps to understand this:

1. Narcolepsy is a neurological disorder that affects the control of sleep and wakefulness.

2. People with narcolepsy experience excessive daytime sleepiness and intermittent, uncontrollable episodes of falling asleep during the daytime.

3. These sudden sleep attacks may occur during any type of activity at any time of the day.

4. In a typical sleep cycle, we initially enter the early stages of sleep followed by deeper sleep stages and ultimately (after about 90 minutes) rapid eye movement (REM) sleep.

5. For people suffering from narcolepsy, REM sleep occurs almost immediately in the sleep cycle, as well as periodically during the waking hours.

6. It is in REM sleep that we can experience dreams and muscle paralysis, which explains some of the symptoms of narcolepsy.

7. Narcolepsy usually begins between the ages of 15 and 25, but it can become apparent at any age. In many cases, narcolepsy is undiagnosed and, therefore, untreated.