Fatigue can be either physiological or subjective. Physiological fatigue reflects the body’s need for replenishment and restoration. It is tied in with factors, such as recent physical activity, current health, consumption of alcohol and with circadian rhythms. It can only be satisfied by rest and eventually, a period of sleep. Subjective fatigue is an individual’s perception of how sleepy they feel. This is not only affected by when they last slept and how good the sleep was but other factors, such as degree of motivation.
Fatigue is typically caused by delayed sleep, sleep loss, de-synchronisation of normal circadian rhythms and concentrated periods of physical or mental stress or exertion.
In the workplace, working long hours, working during normal sleep hours and working on rotating shift schedules all produce fatigue to some extent.
Symptoms of fatigue (in no particular order) may include:
- Diminished perception (vision, hearing, etc.) and a general lack of awareness;
- Diminished motor skills and slow reactions;
- Problems with short-term memory;
- Channelled concentration – fixation on a single possibly unimportant issue, to the neglect of others and failing to maintain an overview;
- Being easily distracted by unimportant matters;
- Poor judgement and decision making leading to increased mistakes;
- Abnormal moods – erratic changes in mood, depressed, periodically elated and energetic;
- Diminished standards.
Most individuals need approximately eight hours sleep in a 24 hour period, although some individuals will know that they need more or less than this to be fully refreshed. People can usually perform adequately with less that eight hours sleep for a few days, building up a temporary sleep deficit. However, any sleep deficit will need to be made up, otherwise performance will start to suffer.
Napping improves mental performance. A 20 minute nap can give 2 hours of good alertness level. When napping it is important to avoid sleep inertia, Sleep inertia is a short term mental confusion that occurs in the transition between napping and being awake, in that it can cause confusion on wakening. Sleep inertia can last 5 to 15 minutes. It is best therefore upon waking from a nap to allow yourself this time to become fully awake before making any decisions. Sleep inertia has been known to last many hours dependent on the amount of sleep deprivation you are suffering at the time.
Choosing the time to take a nap is also important. For example an afternoon nap can influence your next sleep pattern resulting in a possible delay in the onset of sleep whereas a morning nap does not normally have an impact on your next normal sleep pattern.