mind during REM periods, as, according to this theory, the forebrain then creates a story in an attempt to reconcile and make sense of the nonsensical sensory information presented to it. This would explain the odd nature of many dreams. Disorders Insomnia Insomnia is a general term for difficulty falling asleep and/or staying asleep. Insomnia is the most common sleep problem, with many adults reporting occasional insomnia, and 10–15% reporting a chronic condition. Insomnia can have many different causes, including psychological stress, a poor sleep environment, an inconsistent sleep schedule, or excessive mental or physical stimulation in the hours before bedtime. Insomnia is often treated through behavioral changes like keeping a regular sleep schedule, avoiding stimulating or stressful activities before bedtime, and cutting down on stimulants such as caffeine. The sleep environment may be improved by installing heavy drapes to shut out all sunlight, and keeping computers, televisions, and work materials out of the sleeping area. A 2010 review of published scientific research suggested that exercise generally improves sleep for most people, and helps sleep disorders such as insomnia. The optimum time to exercise may be 4 to 8 hours before bedtime, though exercise at any time of day is beneficial, with the exception of heavy exercise taken shortly before bedtime, which may disturb sleep. However, there is insufficient evidence to draw detailed conclusions about the relationship between exercise and sleep. Nonbenzodiazepine sleeping medications such as Ambien, Imovane, and Lunesta (also known as "Z-drugs"), while initially believed to be better and safer than earlier generations of including benzodiazepine are now known to be almost entirely the same as benzodiazepines in terms of their pharmacodynamics, differing only at the molecular level in their chemical structure, and therefore exhibit similar benefits, side-effects, and risks. White noise appears to be a promising treatment for insomnia. Sleep health Low quality sleep has been linked with health conditions like cardiovascular disease, obesity, and mental illness. While poor sleep is common among those with cardiovascular disease, some research indicates that poor sleep can be a contributing cause. Short sleep duration of less than seven hours is correlated with coronary heart disease and increased risk of death from coronary heart disease. Sleep duration greater than nine hours is also correlated with coronary heart disease, as well as stroke and cardiovascular events. In both children and adults, short sleep duration is associated with an increased risk of obesity,