Yes man, it is definitely one of the scariest things I have experienced. I get it about 1-2 times per month. I saw the old hag as well, almost the exact same experience you had.

A lot of people think they experience it fully but it isn't super common and most people will only get it once in their life, typically if you experience more than this its called recurring sleep paralysis. I have had some friends tell me they had it and seemed pretty calm in describing it, however when one really goes through this it is a pretty traumatizing experience.