For many people, sleep is a welcome end to a long day. We climb into our beds to restore our energy and prepare us for the day to come. It is so vital, in fact, that the average person will spend a third of their life sleeping. While there are many theories, research has yet to find a conclusive reason for our need to sleep. What they do know is that disrupted or the lack of sleep can be extremely distressing, and in rare cases, even fatal. Most of us have experienced trouble sleeping at one time or another, which may interrupt one or more of these types of sleep. However, for some, trouble sleeping can become habitual, to the point it causes significant distress in an individual's life. These challenges may be due to difficulty falling asleep, intense nightmares, breathing issues, or the effects of a substance or medication. They can even continue into the day, affecting or interrupting an individual's wakeful period. If any of these appear to be the case, the individual may have a sleep disorder, also called a sleep-wake disorder. Because sleep is so vital to our experiences as human beings, individuals with sleep-wake disorders may find these disturbances go well beyond their periods of sleep, negatively affecting every aspect of their lives.