Excessive daytime sleepiness (EDS for short) is the most frequent problem that people report when they visit a sleep clinic. It is often thought of as a normal part of everyday life and commonly confused with fatigue, although fatigue includes having very low energy and requiring rest, but not necessarily needing sleep. While everyone experiences sleepiness from time to time, persistent EDS often signalizes a deeper issue and is regarded as a symptom of most sleep disorders and many non-sleep-related conditions. Depending on how consistently this problem happens, for how long and how intensely, it could be a minor annoyance or a major problem in one’s life. EDS lowers one’s alertness level, memory, focus, and cognitive functions, among other things. In milder amounts, sleepiness could affect one’s schedule, make them slower, sloppier and otherwise reduce their standard abilities; in more consistent, excessive measures, it could temporarily debilitate the person to an extent and make a struggle out of regular daily chores and activities. When one has to be present and attentive while having difficulties even staying awake, a lot is at stake; the task they are performing, theirs and other people’s safety can be compromised during even seconds of a bad sleepiness spell.

With this in mind, doctors at sleep clinics have standardized a few different procedures to measure the patients’ sleepiness levels as accurately as possible – and this is no simple task. Sleepiness is a subjective feeling, and it’s hard to assess precisely. How sleepy is too sleepy? Even so, subjective tests still find their purpose in many sleep clinics and even on the internet, because of their time-efficiency and ease of access. These tests are meant to be only the first step in a diagnostic procedure, and they serve as a general overview of the patient’s situation and a good introduction into other potential examination steps. Other than that, the patients can use the test to get some hang of the subject as they face sleep issues for the first time; knowing what they can expect at the first doctor’s appointment helps some people take the step of scheduling one.

One such a subjective test that we will focus on in this article is called the Stanford sleepiness scale.

What is the Stanford Sleepiness Scale?

The Stanford sleepiness scale, or SSS for short, is one of the few (and the oldest) self-report methods for assessing one’s sleepiness levels throughout the day. Now widely available online and simple enough for anyone to comprehend, SSS is designed to measure sleepiness in a range from 1-7, 1 representing complete alertness and 7 standing for excessive sleepiness or being barely awake. This test takes mere minutes to complete and is used to determine one’s alertness level at any hour of the day, taking into consideration that during this timeframe, there are normally some oscillations; usually, approximately 9 A.M. and 9 P.M. mark the peak of one’s alertness, with some sleepier times in between.

The slight dip in our energy in the afternoon, just after we’ve had lunch is nothing to get alarmed about but exhaustion at the point of the day when one’s supposed to be most alert signals a problem that needs to get addressed with professional help. SSS can be handy even for people whose sleepiness level doesn’t reach the “excessive” score. With this information in mind, a person can know when to expect to be more drowsy and avoid doing important tasks that require focus at those times, and leave them for a more “sober” point of the day, thus taking full advantage of their natural alertness cycle.

How the SSS Rates Sleepiness?

The degrees of sleepiness you can score on this test are:

  1.    Feeling alert, wide awake, or active
  2.    Functioning at high (but not peak) levels; able to concentrate
  3.    Relaxed and awake; responsive without being fully alert
  4.    A bit foggy and let down
  5.    Foggy; slowed down; not interested in staying awake
  6.    Woozy, sleepy, fighting sleep
  7.    Not fighting sleep; dream-like thoughts

The first three answers indicate that you are (relatively) alert; anything below, and you are unfocused at best, exhausted at worst. Depending on what time of day you did the test and how high you rated your sleepiness level, results can mean different things. For example, if you took the test around 3 P.M. and felt somewhat foggy (4), this doesn’t indicate something is wrong just yet. Being less alert at that time of day is normal, especially if you have been working hard for hours, or had a big meal. However, if it’s been only a couple of hours since you woke up, the time when you are supposed to be most alert, and you assess your sleepiness with a 4, this is definitely something to worry about; the bigger the number you pick, the bigger the sleep debt you have to make up for.

You might very well be aware of the cause of your sleep deprivation – maybe you stayed up late but had to get up early regardless. One day of being sleepy, especially in a situation like that, still doesn’t signify anything out of the ordinary. Even if it repeated through the entire week or two, it doesn’t mean a disorder has developed. But if you purposely went online to look for a sleepiness test, or went to a sleep clinic, chances are you are worried that something might be wrong. Feeling foggy and slow most of the time indicates the possibility of a sleep disorder or some other medical condition. In that case, further examination is required: your doctor might give you another, more detailed questionnaire to fill out, introduce you to writing a sleep journal, order polysomnography, and so forth (we will cover some of these in more detail later). Only after a few of these tests have been performed will your doctor be able to rule out enough disorders to eventually diagnose you. A single test, especially a vague, subjective one like SSS, is never going to present the entire picture. Which brings us to…

Criticism of the SSS

You saw it coming. This testing method has a few faults. To start with, it is subjective. This fact doesn’t automatically discredit SSS and similar tests; as mentioned above, there is a certain value in this method, at least enough for it to still be used. However, doctors need to have more backed information to work with than a patient claiming to feel sleepy. This is never guaranteed with a one-question method like the SSS because it also requires the patient to have some degree of awareness of the subject, and of their own state, which isn’t always the case.

Further, the SSS has been criticized for being unidimensional; that is, it doesn’t differentiate between a person with a sleep disorder and a person who just happens to be sleepy at the time of the test. It requires a special context to give satisfying results, but even as such is useful for repeated check-ups on the patient during treatment, or after.

Because of these points, SSS has been validated for use only in population over the age of 18, and overall remains useful as a way to open up the conversation about sleep with a patient and keep track of their progress, more than as a primary diagnostic tool. Excessive sleepiness is just one symptom to look for when identifying potential sleep disorder. There are far more reliable and wider-range diagnostic methods to choose from when it comes to sleepiness and sleep-related disorders.

Some common methods for diagnosing sleep disorders

  •         Physical examination. After taking a medical history, a brief physical examination often follows. It might include blood and urine tests if a doctor deems it necessary, usually to check for a suspected issue with the thyroid function, potential iron deficiency or diabetes, as well as to rule out some other medical and psychiatric conditions discoverable by these lab tests.
  •         Multiple sleep latency test (MSLT) is a widely used test that measures how fast a person falls asleep when given the opportunity for a short nap after a good night’s sleep, along with whether they reach the REM stage during this time or not. If they fall asleep faster than the average or manage to enter the REM stage, it is a good indication of excessive daytime sleepiness and a potential sleep disorder, like narcolepsy. Some other tests worth mentioning include the Epworth Sleepiness Scale, Pittsburgh Sleep Quality Index, and Fatigue Severity Scale.
  •        Actigraphy is a method for measuring movement during the patient’s sleep. It works by setting up a small device for the patient to wear around the wrist or ankle for at least a week. It is usually ordered if polysomnography isn’t available, as a smaller-scale sleep study, and finds particular use in diagnosing delayed sleep-wake phase disorder.
  •         Polysomnography. This sleep study is done in a laboratory usually at night and with the supervision of a specialist. It measures the patient’s brain wave activity, eye movements, heart rhythm, breathing functions and more during sleep. It is the only definitive method for diagnosing some disorders like sleep apnea. However, tests like this one take time and aren’t cost-efficient for patients whose disorders aren’t severe, or for patients whose main issue is insomnia, so doctors often try out other options first.


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