Look up sleep paralysis or rem atonia, these both explain what happened to you. Sleep paralysis more accurately describes a disorder in which you have this happen to you many times throughout your life--it is normal for you to experience it a few times in your lifetime, but if it happens more than once a month you need to speak to a doctor. Rem atonia is the mind and bodily state in which the disorder of sleep paralysis occurs. It is a regular function of sleep and should not worry you. If it is induced, it is in my opinion fine to be called either, but ever since more information on the subject has come out, people on the website tend to be a little anal in the terminology you use, and so I guess it is more technically correct to use "rem atonia" when speaking about times you have induced the state. In the past, I induced it many times, I'd say a good 15 to 20 times. When I was actively lucid dreaming, I would also occasionally wake up in the state after dreaming, but I liked the experience so it wasn't scary to me. Then again, I've never had a demon or old witch hag sitting on my chest and choking me so I guess it's only natural I did not ever find the experience scary. However, especially when you do not mean to induce it, the "old hag" or demons that prevent you from breathing and pretty much send you in a state of terror and being unable to move your body but move your eyes is very common.