Hypocretin is a protein secreted by the hypothalamus which regulates sleep and wakefulness. A lack of this protein is thought to cause narcolepsy and cataplexy. Evidently, if there is a lack of this protein, then the body will not be able to differentiate as efficiently between sleep and wakefulness, hence the excessive daytime sleepiness and the lack of control over this sleepiness. There are drugs available that can help aid replacements for this protein.