“Overall, about 1 in 2,000 people in the United States may have narcolepsy. The actual number of people who it affects may be higher. This is because the symptoms can be similar to other sleep disorders, such as obstructive sleep apnea.

Narcolepsy develops as a result of changes in the hypothalamus region of your brain, basically. This small gland is located above your brain stem.

The hypothalamus helps regulate the release of hormones that affect numerous parts of your body. For example, it’s responsible for releasing hypocretins, which help regulate sleep.

Hypocretin neurons help regulate your sleep-wake cycles. These chemicals in your brain are at their highest levels when you’re awake. They naturally decrease during your normal bedtime.

But when you have narcolepsy, hypocretin releases are low. This causes disruptions during the daytime, such as excessive sleepiness and fatigue. You may also tend to take more naps during the day.

Reduced hypocretins are strongly linked to narcolepsy type 1. This type of narcolepsy includes:

• disrupted sleep cycles
• daytime fatigue
• cataplexy (sudden loss of muscle control)

A rare form of narcolepsy can develop as a result of   damage to the hypothalamus from a brain injury. This is known as secondary narcolepsy.

Secondary narcolepsy is a severe neurological condition that can lead to irregular sleep cycles as well as memory loss and mood disorders.   If you have type 2 narcolepsy, you may experience issues with sleep cycle regulation but don’t   have issues with cataplexy.  The cause of type 2 narcolepsy is unclear.”

Healthline (https://www.healthline.com/health/narcolepsy/narcolepsy-and-your-brain#brain-chemicals)