Excessive daytime sleepiness is a symptom of most sleep disorders (including insomnia, apnea, and circadian disorders) and a major detriment to quality of life.
You might think: isn’t excessive daytime sleepiness a made-up problem? An attempt to medicalize a normal part of human experience? And isn’t "excessive" subjective?
No. The medical world uses the term excessive daytime sleepiness (EDS) to get a handle on a very real problem experienced by millions. Defining a situation is the first step to managing it. Yes, people have had excessive sleepiness since the Stone Age and it is a medicalization of a routine part of human life, but that doesn’t mean it isn’t a valid medical description of something that is worth looking into and possibly treating.
While it is true that excessive is subjective, so is much else in medicine that doctors are called to diagnose. There are some tests – not blood or urine tests but behavioral tests – that can be employed to get a handle on the level of sleepiness. They are not perfect, but they have proven useful enough to help doctors. The Johns Scale of Drowsiness, the Epworth Sleep Scale, the Maintenance of Wakefulness Test, the Stanford Sleepiness Scale – all these are used in diagnosis of sleep disorders. The psychomotor vigilance test is useful for quantifying impairment due to EDS. There is no set number for what constitutes "excessive" sleepiness on any of these tests. Some medical practitioners use a pupillography sleepiness test. Doctors use them in conjunction with other indicators. A medical history is useful in diagnosing EDS, although doctors have to understand that patients may have different language than medical texts: they might complain about being tired all the time or fatigued, rather than sleepy. Some patients with EDS may be reluctant to admit they are sleepy at all, seeing it as a sign of laziness or a moral failing.
Insomnia can result in excessive daytime sleepiness, as can many neurological conditions and illnesses. Traumatic brain injuries (which include strokes), narcolepsy, poisoning, Parkinson’s, Alzheimer's, and other forms of dementia and general cognitive decline can result in excessive daytime sleepiness. Type 2 diabetics and people with apnea, depression, and asthmas tend to have greater incidence of EDS. A recent study found 47% of TBI patients had EDS and TBI patients are at high risk for sleep disorders. Medicines also can produce EDS – the warning labels of many mention risk of drowsiness. There are so many common causes of sleepiness that some estimate as much as 20% of the population suffers excessive daytime sleepiness. The resulting loss of human potential caused by lowered mental acuity is enormous.
The neurotransmitter adenosine is secreted during waking and builds up over the day. It is part of the homeostatic sleep process and the hypothalamus part of the brain has been found to be rich in neurons that produce adenosine. (These cells project into other parts of the brain including the cortex)
People with EDS are more likely to have automobile accidents or industrial accidents on the job. They do worse in school and on big tests and are less productive in office work. They are irritable. It is one of those underappreciated, ubiquitous things that saps the potential of our society.
EDS makes life’s problems worse. It makes depressed people more depressed. It makes it more difficult to fight through minor irritations and to cope with challenges. It reduces the amount of exercise people get. It shortens the lifespans in older people with diseases.
As with insomnia, EDS is often overlooked by doctors or misinterpreted. Patients might complain about being tired which is not the same as being sleepy. Note that fatigue is not the same as sleepiness. You can get fatigued after exercise of the body, but not necessarily drowsy. Fatigue manifests as a lack of motivation and energy. Sleepiness is a physiological state is which the person feels the need to sleep. Lack of sleep can make a person fatigued, and so can other mental processes and phenomena. Fatigue is a common symptom of many illnesses and conditions.
Good regular sleep is the first thing to try in hopes that the EDS will disappear. That includes attention to sleep hygiene and, if necessary, medicines to ensure sufficient sleep. If those interventions don't work, some doctors and patients may opt for stimulants to make the daytime sleepiness go away.
Which stimulants? The amphetamine Dextroamphetamine and the ADHD medication Methylphenidate (Ritalin) are sometimes prescribed. Modafinil is becoming the go-to stimulant for EDS in recent years because of its low side effect profile. Sodium oxybate (GABA) is used only very bad cases.
Caffeine works. It is not a placebo effect. Repeated controlled studies have found administration of caffeine reduces sleep propensity and improves performance on vigilance tests. Further, when the subject stops taking the caffeine for a day (is given a placebo), these effects disappear.
The detailed biological causes of sleepiness are unknown, as is so much about sleep and waking. Does sleepiness reflect a failure of the brain’s process in maintaining wakefulness or is it a separate process that fights wakefulness and takes over the brain? Scientists are unraveling the neurological substrates of sleepiness, such as the discovery of the orexin system, but much remains unknown.
Naps combat EDS and are a remedy in many situations. Naps can be a good idea even for people who don’t have formal EDS to increase mental performance in the afternoons.
Note also that the body has rhythms and it is common to have a "dip" in the early afternoon. This normal afternoon sleepiness does not count as excessive daytime sleepiness in a clinical sense.
Some people with EDS experience sleepiness in short spurts of heavy sleepiness or lack of concentration. Some may even fall asleep unintentionally during the day. Unplanned sleep periods could be very short (microsleeps) or turn into naps.