I had never heard of such a thing before. Sleep Paralysis. But once a friend told me about it and my research of the subject confirmed that it's an ancient occurrence in people's lives (indeed, the word nightmare itself is derived from the phenomena!) I became obsessed by it. Part of this obsession was because I realised it had happened to me once, when I was a small child of 8 or 9 years. I'd woken up from a really bad nightmare and saw, what I thought was, the silhouette of my brother and mother standing over me in the dark, looking down. Their presence made me happy, "Thank God they're here right after a nightmare", but as soon as I finished that thought the silhouettes stretched out their hands and started choking me. I immediately woke up. I'd had sleep paralysis in the shape of two demons. This is not unusual for people who have sleep paralysis and artists renditions of this particular type was what made me realise that that is what happened...