Nightmare disorder, also known as "dream anxiety disorder", is a sleep disorder characterized by frequent nightmares. The nightmares, which often portray the individual in a situation that jeopardizes their life or personal safety, usually occur during the second half of the sleeping process, called the REM stage. Though such nightmares occur within many people, those with nightmare disorder experience them with a greater frequency. The disorder's DSM-IV number is 307.47.