Sleep is a naturally recurring state characterized by reduced or lacking consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles
(the need for sleep as a function of the amount of time elapsed since the last adequate sleep episode) must be balanced against the circadian element for satisfactory sleep
get a good nights sleep. Sleep problems such as sleep apnea, sleep deprivation, insomnia, restless leg syndrome, snoring, sleepwalking, and moreThe importance of sleep is underscored by the symptoms experienced by those suffering from sleep problems. People suffering from sleep disorders do not get adequate or restorative sleep, and sleep deprivation is associated with a number of both physical and emotional disturbances. In addition, sleep is influenced by the circadian rhythms (regular body changes in mental and physical characteristics that occur in the course of about 24 hours).
Sleep typically occurs in cycles that range from 90 to 120 minutes in length, with 4-5 cycles occurring during each night's sleep. In the first half of the night, there is a transition from wakefulness into stage N1 sleep, then to stages N2, and N3. Stages N2 and N3 then reappear, followed by the first instance of REM sleep. Cycles of stage N2 and REM sleep alternate with each other for the second half of the night.
In Hans Christian Andersen's fairytale The Princess and the Pea,
a princess is unable to get a good night's sleep because a pea has been
placed under her mattress—which is actually 20 mattresses piled high!
One moral to this tale is that the quality of what you sleep on matters
to the quality of your sleep. In fact, when we are asleep, our body is
compressed by gravity in a different way than when we stand upright, and
we need to be fully supported by the mattress and its supporting
structures. For this reason, the mattress has been called an
"anti-gravity machine" that makes it possible to maintain the natural
shape of the spine when sleeping.[1]
Although we spend around one-third of our life lying on mattresses,
and although it is estimated that about half of all Americans experience
at least occasional sleep difficulties, there has been relatively
little scientific study of mattress design.[2] Poor mattress design can
create inappropriate body support, and this in turn may cause muscle
discomfort and back pain.[3] So what are the features of a good
mattress? Does it matter if it's too hard or too soft? Does it matter if
it's an orthopaedic mattress? Is a mattress even important? Recent Mattress Study
In a recent study of mattress ergonomics that tested 12 women, lying on
an incompressible wooden surface was compared with various mattresses.
All of the mattresses were judged as significantly more comfortable than
the wooden surface, but there were no significant differences between
mattress types, even though these included orthopaedic and normal
designs. Measures of shoulder, elbow, hip, knee and ankle body contact
pressures showed few significant differences, and surprisingly, there
were no significant associations between measures and the comfort
ratings.[4]
However, how hard or soft a mattress feels is thought to be an
important factor in reducing or preventing back pain.[5] Comparison of
sleeping on a futon or a softer air mattress showed that sleep onset
latency, waking after sleep onset, and the sleep efficiency index were
comparable for both mattresses, but subjective sleep evaluation tended
to be better for the air mattress.[6] A study of sleep quality and bed
firmness showed that 4 of 9 male subjects slept significantly better on
the softer mattresses, while 2 slept better on the harder mattress. The
greatest difference in sleep quality occurred when changing from the
subject's own mattress to one of the test mattresses, and the authors
concluded that it may take several days to adapt to a new sleep
surface.[7] This may be why business travelers often report sleep
difficulties.[8]
