Daytime sleepiness is the propensity to fall asleep at inappropriate times during the day.
The degree of daytime sleepiness correlates directly to the amount and quality of sleep during the previous night. The duration people need to stay awake varies with each individual; but surveys and research indicate most people perform optimally with 7.5 – 8.5 hours. Any sleep loss leads to immediate sleepiness. By the same token, the opposite is true: An extension of sleep duration can alleviate drowsiness and improve performance.
Sleep quality also counts, though this aspect is usually less obvious. Sleep fragmentation (in other words, the lack of continuity) impacts sleep quality and causes drowsiness. There are many possible causes: sleep-related breathing disorders, periodic limb movement during sleep, other medical ailments accompanied by pain or discomfort (e.g., arthritis, back pain, fibromyalgia), and narcolepsy. And that’s far from a complete list.
Individuals are sometimes unaware of their own daytime sleepiness. It may come to their attention after trying to cope with other problems such as decreased performance, hypertension, excessive weight, snoring, and mood disorders.
Fortunately, good objective tests for measuring sleepiness are available. The Multiple Sleep Latency Test (MSLT) and the Maintenance of Wakefulness Test (MWT) are commonly used for this purpose.
Scientifically-validated questionnaires such as the Epworth Sleepiness Scale (ESS) and the Stanford Sleepiness Scale (SSS) are also useful for evaluating sleepiness. As well, alertness can be measured using a visual analog scale (VAS).
If daytime sleepiness is present, the underlying cause(s) should be investigated and identified. Appropriate treatment(s) or lifestyle changes can improve sleep duration and quality, thereby leading to better health, improved performance, and a new sense of wellbeing.