- nocturia or nycturia, interrupted sleep due to the frequent need to get up to urinate during the night, particularly common in pregnant women and the elderly.
- bed-wetting or enuresis, uncontrolled urination during sleep, especially prevalent in young children, which may be caused by an insufficient supply of the antidiuretic hormone ADH, a small bladder combined with long sleep periods, or other physical or emotional problems.
- hypnophobia or somniphobia, an anxiety disorder manifesting as an abnormal fear of sleeping or going to bed, a psychological state perpetuated by self-induced stress and anxiety (also known as negative sleep conditioning).
- nocturnal dissociative disorder, a psychiatric disorder of wakefulness , superficially similar to sleep-walking, in which a sufferer wanders off or acts out scenarios while technically awake (although completely unaware of their actions, and with no subsequent memory of them), usually as a psychological response to earlier abuse or trauma.
- encephalitis lethargica, an extremely rare viral infection of the sleep-wake cycle mechanisms in the hypothalamus, causing extreme lethargy, sleep period inversion, even catatonia or a completely unresponsive coma-like state.
Many other superficially unconnected medical or psychological conditions have nevertheless been closely linked with sleep problems. It is, however, not always clear where the causal relationship lies: in some cases, the conditions lead to sleep problems; in other cases, the opposite is true, and long-term sleep disorders can actually cause the conditions; occasionally, both may occur, in a spiral of positive reinforcement.
Some or the better-known diseases and conditions that fall into this category include the following:
- Alzheimerís disease (AD), and other kinds of dementia, which in their early stages may be characterized by excessive sleeping (hypersomnia), and in their later stages may be marked by insufficient sleep or insomnia, with nighttime sleep being ultimately replaced by short irregular dozes throughout the day and night more remniscent of irregular sleep-wake rhythm disorder (ISWRD) or polyphasic sleep (in dementia patients, the number of neurons in the circadian pacemaker becomes substantially reduced, so that circadian rhythms may be severely disrupted).
- Anxiety (and other related mood disorders), which typically leads to difficulty falling asleep and staying asleep throughout the night.
- Asthma, particularly nocturnal asthma, in which asthma symptoms worsen at night, so that coughing, wheezing and breathlessness disrupt sleep.
- Attention deficit hyperactivity disorder (ADHD), whose incidence and symptoms in children show marked overlaps with those of sleep disorders. Sleep disorders in children are often misdiagnosed as ADHD (and vice versa), and some recent research has also suggested that sleep's role in the brain's consolidation of emotional memories in particular may be linked to ADHD symptoms.
- Autism Spectrum Disorders affect an estimated 1 in 150-160 children, and half to three-quarters of them typically develop sleep disorders of some kind. Others appear to be able to function more or less normally on significantly reduced hours of sleep. Some have theorized that children with autism produce less melatonin in their brains, or do not produce it at normal times, possibly due to genetic mutations (the gene and enzyme ASMT, which is known to be involved in the production of melatonin, has been specifically flagged in this respect). Another possible link stems from iron deficiency, a common problem in autistic children, which may lead to sleep disorders like restless legs syndrome.
- Depression, which is often accompanied by insomnia or similar symptoms (especially waking up too early in the morning), or sometimes the opposite, hypersomnia-like symptoms. Those suffering from depression tend to experience REM sleep much earlier in their sleep cycles than normal, suggesting some disruption in the drive-regulation function. REM deprivation, by means of antidepressant medication, may fix this sleep stage abnormality, as well as relieving the waking symptoms of depressives. Depression shares many risk factors and biological features with various different sleep disorders, and misdiagnosis is common.
- Diabetes, specifically type II diabetes, which can be precipitated by sleep deprivation-driven changes in the balance of hormones that regulate appetite, leading to overeating, higher glucose levels and insulin resistance, all of which are risk factors for type II diabetes.
- Multiple sclerosis (MS), which tends to bring with it a variety of sleep disorders including insomnia, restless legs syndrome, narcolepsy, REM sleep behaviour disorder, and others.
- Epilepsy, as well as the drugs typically used to treat it, appear to be inherently implicated in sleep disorders. In fact, epilepsy disturbs sleep and sleep deprivation aggravates epilepsy, in a two-way connection. Epilepsy sufferers may or may not have seizures at night depending on the type of epilepsy (for some people, seizures may occur exclusively during sleep), and they are also more prone to sleep apnea.
- Obesity, which is a major contributing factor to sleep disorders like sleep apnea, but also a common consequence of many sleep disorders, through their effect on metabolism and hormonally-increased appetite.
- Parkinsonís disease (PD), which has been linked with several sleep disorders, including insomnia, REM sleep behaviour disorder, periodic leg movement disorder, restless legs syndrome, sleep apnea, narcolepsy, etc.
- Schizophrenia, for which sleep disorders are one of the most common indications (affecting some 30%-80% of patients). An improvement in sleep quality is frequently correlated with an improvement in negative symptoms in schizophrenics.
- Seasonal affective disorder (SAD), also known as winter depression, which is triggered by the desynchronization of circadian rhythms during the shorter days of fall and winter.
Snoring is not a sleep disorder as such, but it can lead to disrupted sleep patterns in some extreme cases. An estimated 45% or people snore at least occasionally, and 25% snore regularly. The noise of snoring can rise to as much as 80-90 dB - equivalent to a large truck or motorcycle passing - and severe snoring can disturb the snorerís own sleep (as well as that of their sleeping partner), even if it is not part of another disorder such as sleep apnea. See the separate section on Snoring for more details.