The<unk>  (Henry Fuseli, 1781) Scientific research shows that<unk> s may have many causes. In a study focusing on children, researchers were able to conclude that<unk> s directly correlate with the stress in children's lives. Children who experienced the death of a family member or a close friend or know someone with a chronic illness have more frequent<unk> s than those who are only faced with stress from school or stress from social aspects of daily life. A study researching the causes of<unk> s focuses on patients who have sleep apnea. The study was conducted to determine whether or not<unk> s may be caused by sleep apnea, or being unable to breathe. In the nineteenth century, authors believed that<unk> s were caused by not having enough oxygen, therefore it was believed that those with sleep apnea had more frequent<unk> s than those without it. The results actually showed that healthy people have more<unk> s than the sleep apnea patients. Another study supports the hypothesis. In this study, 48 patients (aged 20–85 yrs) with obstructive airways disease (OAD), including 21 with and 27 without asthma, were compared with 149 sex- and age-matched controls without respiratory disease. OAD subjects with asthma reported approximately 3 times as many<unk> s as controls or OAD subjects without asthma. The evolutionary purpose of<unk> s then could be a mechanism to awaken a person who is in danger. Lucid-dreaming advocate Stephen LaBerge has outlined a possible reason for how dreams are formulated and why<unk> s occur. To LaBerge, a dream starts with an individual thought or scene, such as walking down a dimly lit street. Since dreams are not predetermined, the brain responds to the situation by either thinking a good thought or a bad thought, and the dream framework follows from there. If bad thoughts in a dream are more prominent than good thoughts, the dream may proceed to be a<unk> . There is a view, possibly featured in the story A Christmas Carol, that eating cheese before sleep can cause<unk> s, but there is little scientific evidence for this.
Nightmare
Night terror  Night terror  1
Nightscout
Twilight sleep
Sleep onset
Mental health day
Yawn
Sleep sex