Information should be added about a person lying in supine position increasing the likeliness of experiencing sleep paralysis.
If someone can find information on substances, presumably oneirogens, predisposing a person to sleep paralysis, it would make for an ideal edit. I personally have experienced SP with hallucinations, both hypnagogic and hypnompompic, as a side effect of low doses (30 mg) of Amitriptyline (Elavil), but I can't add that to the article because I'd be contributing to original research.
Caffeine, stress, and an irregular sleep schedule additionally predispose a person to SP.
Since this is a site dedicated to psychonautics, it may be ideal to add information about the steps a person can take to intentionally induce sleep paralysis, which is available on numerous other websites.