Sleep deprivation
<p><b >Sleep deprivation</b> is the condition of not having enough <a href="http://en.wikipedia.org/wiki/Sleep" title="Sleep" >sleep</a>; it can be either <a href="http://en.wikipedia.org/wiki/Chronic(medicine)" title="Chronic (medicine)" >chronic</a> or <a href="http://en.wikipedia.org/wiki/Acute(medicine)" title="Acute (medicine)" >acute</a>. A chronic sleep-restricted state can cause <a href="http://en.wikipedia.org/wiki/Fatigue_(medical)" title="Fatigue (medical)" >fatigue</a>, daytime sleepiness, clumsiness and weight loss or weight gain.<sup id="cite_ref-RatExperiments_0-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Sleep_deprivation#cite_note-RatExperiments-0" >[1]</a></sup> It adversely <a href="http://en.wikipedia.org/wiki/Effects_of_sleep_deprivation_on_cognitive_performance" title="Effects of sleep deprivation on cognitive performance" >affects the brain and cognitive function</a>.<sup id="cite_ref-Alhola_1-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Sleep_deprivation#cite_note-Alhola-1" >[2]</a></sup> Few studies have compared the effects of acute total sleep deprivation and chronic partial sleep restriction.<sup id="cite_ref-Alhola_1-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Sleep_deprivation#cite_note-Alhola-1" >[2]</a></sup>Complete absence of sleep over long periods is impossible for humans to achieve (unless they suffer from <a href="http://en.wikipedia.org/wiki/Fatal_familial_insomnia" title="Fatal familial insomnia" >fatal familial insomnia</a>); brief <a href="http://en.wikipedia.org/wiki/Microsleep" title="Microsleep" >microsleeps</a> cannot be avoided.<sup id="cite_ref-2" class="reference" ><a href="http://en.wikipedia.org/wiki/Sleep_deprivation#cite_note-2" >[3]</a></sup> Long-term total sleep deprivation has caused death in lab animals.<sup id="cite_ref-3" class="reference" ><a href="http://en.wikipedia.org/wiki/Sleep_deprivation#cite_note-3" >[4]</a></sup></p>