Sleep Paralysis ~ Scientific Explanations And The Old Hag Legends

Sleep Paralysis has been known for a long time. Throughout the history of mankind there have been the reports of people awakening to feel a sense of weight on their chests and an inability to move their limbs to escape this pressure. People who experience this phenomena almost unanimously describe a feeling of panic and fear at their experience which can last long after the paralysis of their bodies has faded and they can move again. Has anyone ever experienced this?