Sleep paralysis in general. Whenever it happens, there’s always some malevolent presence. I had something sitting on my bed, screaming right in my ear or gust being nearby, and you cannot even turn around to look at it or ask for help even if it’s available.
I recognize the type of sleep when it’s likely to happen, the heavy uneasy feeling usually in the morning, and fight to wake up completely to avoid the encounter. But I always know that I’ll have to go back to bed eventually, I can never escape.