Insomnia
While insomnia is a common symptom of depression, antidepressants are effective for treating sleep problems whether or not they are associated with depression. While all antidepressants help regulate sleep, some antidepressants such as amitriptyline, doxepin, mirtazapine, and trazodone can have an immediate sedative effect, and are prescribed to treat insomnia. Amitriptyline and doxepin both have antihistaminergic, anticholinergic, and antiadrenergic properties, which contribute to both their therapeutic effects and side effect profiles, while mirtazapine's side effects are primarily antihistaminergic, and trazodone's side-effects are primarily antiadrenergic. Mirtazapine is known to decrease sleep latency (i.e., the time it takes to fall asleep), promoting sleep efficiency and increasing the total amount of sleeping time in people with both depression and insomnia.
Idiopathic hypersomnia
Idiopathic hypersomnia is a neurological disorder which is characterized primarily by excessive daytime sleepiness (EDS). It has historically been rarely diagnosed and is often very difficult to diagnose at an early stage; it is usually a lifelong chronic disease, which is often debilitating. There is a very low level of public awareness of idiopathic hypersomnia, which often leads to stigma for those who suffer from it. There is currently no cure, but there are several off-label treatments, which are primarily FDA-approved narcolepsy medications. Research funding for its study is scarce.