During an episode a person will become fully awake and able to look around by moving their eyes. However, control of breathing, bodily movement and making sounds are completely inhibited, resulting in a possibly terrifying experience. An episode can last from a several seconds to a few minutes and is sometimes accompanied by vivid hallucinations.
The episode ends when the person falls back asleep peacefully, or the paralysis lifts. The latter often results in violent movement or convulsions along with a shout or scream.
While in this state a person is said to be "Riding with the witch"
It is most often encountered while sleeping in unfamiliar or relatively uncomfortable conditions. Most people will experience some form of this phenomena at least once in their lifetime.
Frank: Nah, I was just riding with the witch, sleep paralysis, ya know?
Chris: Damn son, you should probably get that checked out! You almost gave me a heart attack, shouting and flailing at 3AM!
Frank: yeah, that'll happen…