This sound so scary! Nothing like this has happened to me but, I know it is common enough to be have a few different names like sleep paralysis by the more science-y minded folks and is known as being ridden by a hag in the more esoteric circles. If I were you I would start doing some sort of protection practice. This would really depend on your belief systems but basically praying for protection before sleep and during these events - even if you are only praying in your mind and not out loud. I hope this scary phenomena clears up for you!