Sleepiness, fatigue and impaired concentration
“Why am I tired all the time?”
We all experience poor (or restricted) sleep from time-to-time and therefore are familiar with its consequences on our daytime functioning. Among the most common are fatigue and sleepiness. Although we might use these terms synonymously, they technically refer to different (though clearly related) things. Sleepiness reflects one's propensity to fall asleep (or inability to stay awake), while fatigue refers to lethargy, or an inability to maintain levels of performance on a given task. In studies where healthy subjects have been sleep deprived (totally or partially), both objective and subjective measures of fatigue and sleepiness tend to increase, and for those whose sleep has been restricted in duration (e.g. from 8 to 4 hours) over several days (e.g. 5 days), sleepiness and fatigue have been shown to increase with each day of accumulated sleep loss (Banks et al., 2010). Indeed fatigue may not be fully overcome after a full night of (recovery) sleep.
Often we may experience both fatigue and sleepiness after sleeping poorly, and sometimes we may experience just one of these in isolation. For those with insomnia, fatigue (sometimes also referred to as reduced energy) is the most characteristic daytime complaint. Problems with sleepiness, on the other hand, may not be as common. A recent study assessed daytime sleepiness in patients diagnosed with insomnia disorder (Roehrs et al, 2011). They used what's called the multiple sleep latency test (MSLT). The MSLT involves providing patients with 4 nap opportunities throughout the course of a day. Sleepiness is measured as the time taken to fall asleep during the nap. Interestingly, despite sleeping more than an hour less than healthy control subjects, the night before, patients with insomnia disorder took longer to fall asleep (by about 2 minutes, on average) during the day. This suggests that patients with insomnia have difficulty falling asleep and reducing arousal both during the day and night. On the other hand, sleep apnoea patients, who often report excessive daytime sleepiness, take less time to fall asleep during the MSLT daytime nap, providing objective evidence of increased daytime sleep propensity. This difference can be very important in day-to-day clinical practice; helping medical professionals tease out what sleep disorder an individual may be suffering from.
Both increased sleepiness and fatigue are associated with the inability to concentrate or 'think clearly'. Indeed, along with impaired energy/fatigue and mood, concentration is one of the most common daytime issues reported by patients with insomnia disorder – this is what was found in the recent Great British Sleep Survey. This inability to concentrate might reflect an issue with sustained attention or shifting attention. In studies where sleep-deprived subjects have been tested after sleep loss, it is commonly the case that they will take longer to respond to a stimulus that appears on the screen (and experience more attentional lapses; failing to respond within a certain time interval). A study in insomnia patients found that a complex attention task – where subjects had to respond on a computer screen to the letter 'p' but not the letter 'd' – revealed impairments in reaction time to making this judgment. Intriguingly, patients were treated with a non-pharmacological treatment (which included cognitive behavioral therapy) and found to improve in performance post-treatment.
Indeed, there is emerging evidence that CBT-I improves a wide array of daytime impairments in those with chronic sleep disturbance (Kyle et al., 2010). For example, studies that have investigated health-related quality of life, have found that improvements in night-time sleep, through treatment, have also been accompanied by improvements in daytime functioning, particularly areas that are fatigue-related.