Hi Chrystal, I am am a 33 year old Registered Nurse who has been experiencing this phenomenon since about the age of 11. It is such a part of my life that I don't even think it strange anymore. My own personal opinion, based on what happens to me, is that these are cases of visitations by demons, or evil spirits, or something like that.
Every single visit is accompanied by an intense feeling of evil and threat.
During my very first visit as a child, in terror I prayed for help and was saved by a being of light which actually chased this thing away from me. That never happened again, but it is another reason I am convinced that this is not simply a psychological or perhaps physiological disorder, but a paranormal experience. I would love to communicate with others who have had experiences similar to mine, or who believe as I do that these episodes cannot be merely brushed off as a disorder of the physical body or the brain.