I am atheist but just a few nights ago, I experienced it. Felt like someone climbing up onto my bed and then pressing against my back (I was sleeping on my stomach) and I felt so breathless.
I was also half-conscious, half-unconsicous.
it has happened to me too the exact same thing only i remember i was trying to scream too but there was no voice coming out….
doc told me it was from stress and anxiety