The transmission spontaneously slipped out of park and went into reverse. My safety was close to critically impacted. When it began to roll on its own, I was scooped by the driver door and dragged several yards until the truck impacted another vehicle and came to a stop. I very likely could have been killed. If anyone had been behind the truck they likely could have been killed. The incident resulted in significant damage to my vehicle and the vehicle that it ran into. I have not driven the truck since the incident to reproduce. Police did come out to inspect the accident. Has not gone to dealer yet. There were no warning light, buzzers, etc. completely spontaneous. Note: the vehicle was running when this happened. When I was able to get back in truck the stalk was still in park position