Fact:

• The Terror That Comes in the Night: An Experience-Centered Study of Supernatural Assault Traditions by David Hufford - looks at sleep paralysis folklore and the wide range of people’s experiences, with a New Foundland focus but generally applicable too.
• Abducted: How People Come to Believe They Were Kidnapped by Aliens by Susan Clancy - examines at sleep paralysis’ role in alien abduction cases (as well as other explanations)

Academic papers:

• Cheyne, J.A., Rueffer, S.D. & Newby-Clark, I.R. (1999) “Hypnagogic and Hypnopompic Hallucinations during Sleep Paralysis: Neurological and Cultural Construction of the Night-Mare”. Consciousness and Cognition 8, 319-337.
• de Sá, J.F.R. & Mota-Rolim, S.A. (2016) “Sleep Paralysis in Brazilian Folklore and Other Cultures: A Brief Review”. Frontiers in Psychology 7, 49-56.