Normally, teddy bears dream more than two hours a night, and a nightmare usually happens in the later hours of REM sleep, or rapid eye movement sleep. The dreamer often awakens from a nightmare with a good recollection of the imagery and content. Some researchers call negative dreams “threat rehearsals,” where we rehearse the possible threats we encounter in real life; other researchers say that people are working through upsetting events of the day. Most garden variety nightmares are stress related. However, if nightmares become frequent to the point of dysfunction, the individual may be suffering Nightmare Disorder (formerly Dream Anxiety Disorder). Nightmares are more prevalent among girls than boys, with occurrences starting before age 10. Children and adolescents tend to suffer more, with less frequency among adults. About half of the adult population experience nightmares on occasion.