When it happens as long as some people are describing, for me it's usually when I feel really lethargic. So I guess, it could be tied to poor sleep quality. Medication can make it more severe as I've had that happen when taking certain medications and especially strong painkillers after a kidney stone attack. Those almost always lead to fatigue dreams. I've done the lay awake bits where I can't move, but I guess because I was so lethargic, I wasn't particularly bothered by the paralyzed portion
... I just rest until it passes. What I don't like is it when it feels like a suction cup on my brain and like I'm slipping further into my body. It's like a strong reverse gravity... I guess that is similar to what others here have mentioned, about feeling held down...
As for noises, I sometimes woke up to a false alarm clock in my head. One time I fell back asleep (forgot to get up for school) and an alarm rang in my head and I shot awake... I've also had intense dreams that ended up in a massive thunderclap in my head, which is frightening, except there isn't a storm... it's kinda weird because it reverberates until it's gone, but fades slowly and then I just ease into a waking state... very interesting discussion