Poor sleep is both a symptom and a cause of mental illness. Sleep problems may contribute to the development or prolongation of mental illness by making it more difficult to cope with mental problems.

Sleep disorders are comorbid with many other illnesses; the most common comorbidities with insomnia are mental illnesses. It’s estimated that 40% of insomnia patients and over 45% of hypersomnia patients have a psychiatric condition. On the other hand, people without mental illness have substantially lower rates of insomnia.  It’s a striking enough difference that nobody doubts the tie between sleep disorders and mental illness any more.

When it comes to the sleep they do get, people with mental illness often report that it’s not restorative. They wake up still feeling tired, whether from waking frequently during the night, falling asleep too late, or waking too early. In fact, as we’ll go into in the sections below, many studies show that patients with mental health disorders experiences demonstrable changes to their sleep architecture. Often, the individual spends more time in the lighter, less restorative stages of sleep, and less time in the critically important deep and REM stages of sleep.

Insomniacs on the whole tend to suffer from this problem – getting less sleep overall and spending insufficient time in the deeper parts of sleep. This is what makes the disorder so particularly frustrating: they feel like there is no relief from their discomfort.

This lack of sleep in turn makes it more challenging to cope with the symptoms of their mental illness. The REM stage of sleep provides us with the emotional and cognitive benefits of sleep. With sufficient REM sleep, we feel emotionally balanced, and able to regulate our emotions and make good judgments. Our brain works and processes information as it should. Without it, we’re moodier, prone to irrationality and poor decision-making, and have difficulty remembering things. It’s easy to see how this mindset makes it tough to cope with mental health.

Together, mental illness and insomnia exacerbate the effects of each other, creating a classic negative feedback loop, and once they get started, push the patient in a downward spiral. This makes treatment of both conditions difficult.

Left untreated, the sleep problems associated with mental health disorders can be particularly dangerous. A University of Michigan study found a strong correlation between insomnia and suicide.