It is common for people with depression to experience various sleep disturbances including insomnia, poor sleep efficiency and perception of poor sleep quality. Although these problems are thought of frequently in conjunction with depression, sleep-related disturbances during waking hours have also been shown to be part of the effects depression has on sleep. Regardless of the type, one of the long-term effects of depression is the development of sleep debt, which creates new difficulties.
Insomnia
Insomnia causes both fatigue and sleepiness during the day, as needed restful sleep is not obtained. Some assessments (such as The Insomnia Severity Index) in fact combine these two effects when assessing the impact of depression on sleep.
Depression can cause three types of insomnia--early, middle and late stage insomnia. These labels indicate the phase of sleep which is disrupted. Early stage insomnia interrupts the natural process of falling asleep, middle stage disrupts deep sleep and late stage abruptly ends sleep before the body is fully rested.
Sleep Efficiency
Depression can also effect sleep by reducing the efficacy of the sleep obtained. Sleep is the most naturally efficient way for our minds and bodies to rejuvenate. Sleep is divided into two types: rapid eye movement (REM) and non-rapid eye movement (NREM). Normally, sleep progresses in cycles between REM and NREM sleep throughout the night. Depression interrupts this cycling and results in sleep which does not efficiently rejuvenate us.
Perceived Sleep Quality
Depression also has a negative impact on the perception of sleep quality. People with depression sometimes have no problems with insomnia, but perceive the quality of sleep obtained as poor. Research on objective and subjective measures of sleep quality indicate that depressed people perceive the quality of their sleep as low, even when objective measures (e.g. monitoring for insomnia and REM sleep patterns) show no irregularities. In other words, all of the known processes associated with a good night's sleep are present, but the depressed person perceives the sleep as poor.
Waking Disturbances
A recent study from the American Psychological Association suggests that day-time disturbances such as fatigue and chronic sleepiness are a separate sleep-related problem. This research showed a higher correlation between waking disturbances and depression than between night-time sleeping problems and depression. This research suggests a "two-factor" model of the impact of depression on sleep, with waking effects of depression on sleep as important as the nighttime effects.
Sleep Debt
Sleep debt is the long-term cost of not getting enough sleep. This debt causes physical and emotional fatigue along with irritability. It also creates diminished abilities to perform high-level cognitive functions such as decision-making and problem-solving. Also, as REM sleep has been shown to be important in memory processing, another effect of sleep debt is difficulty recalling information and forming memories, which are essential to learning.
