Normally, we become "comatose" when we sleep... The brain proceeds to dreaming and disconnects temporarily our body control... This is no problem since our conscious mind is temporarily disconnected... In Sleep paralysis, however, in the middle of the dream we suddenly become aware before our brains reconnect our motor control hence the feeling of paralysis and unable to talk... In this specific sense, our brain is like a computer that needs a rebooting time to reconnect the motor control.... Sleep paralysis usually happens when a person is in a lot of stress.