Narcolepsy is caused by severe loss of the orexin-producing neurons in the hypothalamus, and the resulting symptoms of narcolepsy include excessive daytime sleepiness, the occurrence of REM sleep at any time of day, and cataplexy – episodes of muscle atonia during wakefulness that are likely produced by some of the same neural mechanisms that produce atonia during REM sleep (Mahoney et al., 2019). Here, HCRT is linked to narcolepsy.