Sick and Tired: Understanding and Managing Sleep Difficulties in ...

Chapter Two. The Role of Sleep
The Normal Sleep Process
Sleep is considered to be the most important recovery mechanism available to humans,
and good sleep is essential for optimal well-being, daily functioning and health (Morin &
Espie, 2003). Poor sleep quality can lead to increased fatigue, negative mood changes
and in extreme cases, can even lead to impaired immune function (Lorton et al., 2006;
Rogers, Szuba, Staab, Evans, & Dinges, 2001). Even moderate sleep loss is associated
with deficits in alertness and performance on cognitive and physical tasks (Jewett, Dijk,
Kronauer, & Dinges, 1999). The amount people sleep has also been linked with life
expectancy, with too little or too much sleep associated with increased mortality risk
(Doghramji, 2006; Gallicchio & Kalesan, 2009). Sleep may be as important as diet,
exercise and genetics (Hublin, Partinen, Koskenvuo, & Kaprio, 2007).
The sleep process usually consists of five sleep stages; four stages of Non-Rapid Eye
Movement (NREM) sleep, and one stage of Rapid Eye Movement (REM) sleep (Morin
& Espie, 2003). Stage one sleep is a transitional stage, lasting approximately five
minutes, where the body prepares itself for sleep. This stage is a state of drowsiness and
if woken up during this stage, the person may not feel that they have been to sleep at all.
Stage two sleep is a light sleep stage where brain activity, heart rate and breathing slow
down, and muscle tension is reduced. Sleep becomes progressively deeper through
stages three and four (also referred to as slow wave sleep). It is thought that the body
has the opportunity to rejuvenate and repair itself during stage four. From stage four
sleep people then return back through the sleep stages to the lighter stage of sleep (stage
two) before entering REM sleep (stage five). REM sleep is characterised by observed
rapid eye movements as if the person is awake, with increased brain activity, heart rate
and breathing rates. It is thought that this is the stage where dreaming occurs and the
brain processes and stores new information to aid long term memory, although this
remains unclear (Morin, 1993). It has been suggested that the brain blocks signals to the
muscles in this stage to prevent people from acting out their dreams. People move
through each sleep stage in a cycle (see Figure 2, p. 16) lasting approximately 90
minutes which is repeated approximately five times over the course of the night. The
length of each sleep stage within a cycle changes over the course of the night, with most
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