Several circumstances have been identified that are associated with an increased risk of<unk> . These include insomnia,<unk>  deprivation, an erratic<unk>  schedule, stress, and physical fatigue. It is also believed that there may be a genetic component in the development of RISP, because there is a high concurrent incidence of<unk>  in monozygotic twins.<unk> ing in the supine position has been found an especially prominent instigator of<unk> .<unk> ing in the supine position is believed to make the<unk> er more vulnerable to episodes of<unk>  because in this<unk> ing position it is possible for the soft palate to collapse and obstruct the airway. This is a possibility regardless of whether the individual has been diagnosed with<unk>  apnea or not. There may also be a greater rate of microarousals while<unk> ing in the supine position because there is a greater amount of pressure being exerted on the lungs by gravity. While many factors can increase the risk for ISP or RISP, they can be avoided with minor lifestyle changes.
Sleep paralysis
Narcolepsy
Sedation
Night terror
Sleep disorder
Hypokalemic periodic paralysis
Syncope 
Atonic seizure