It is very unpleasant and certainly feels like demonic presence at times. I've experienced sleep paralysis most of my life and fairly frequently.

I learned that taking in a large breath and holding it in will break the freeze and you will wake up in 5-10 seconds, just hold it in. Recently I discovered that sleeping with an Indochinite tektite under the pillow, for some unknown reason, eliminates sleep paralysis completely. I haven't had it since. They are only $5-$10 for the tektites on ebay.