Feeling like I'm dying right before falling into a deep sleep? Anyone experience this? Pls read full description.?

This has happened to me twice now. You know how when you sleep, at some point you just fall asleep and start dreaming then you wake up in the morning? You don't remember falling asleep, and you don't remember the start of your dreams. Its like, at some point when you're fall in asleep, you lose consciousness, then your body fully falls asleep, and you randomly start dreaming but not being aware of falling asleep or srarting the dream. I had two instances where I was conscience all the way up to falling into a deep sleep and starting a dream and it was the scariest thing ever. My body felt SO heavy like i was sunk into my bed. I tried to reach up to feel my heart beat, its was very very slow. I thought I was going to die..I felt like I had to let go in a sense. And that if I let go, i would die, but it would've felt really good. But I was afraid to feel good and let go. So I forced myself awake. But if i let myself go, i just would've ended up dreaming. I wonder if that's what its like to die? Like old people in their sleep who just die of old age..i felt like i almost experienced that. It was so insane and hard to describe in detail..anyone ever experience this?