Narcolepsy
Some scientists think that narcolepsy is caused by a lack of hypocretin. Hypocretin is a chemical in the brain which wakes people up and regulates sleep. However, It is not yet known for sure what causes it. Quite a few sufferers also have another family member with the disease. This may point to the fact that some of the things that cause the disease may be passed from the parents to the children through genes.