Just another symptom of messed up brain.
One of my cats has started sleeping next to my pillow. And I sleep with a stuffed animal (don't judge me!). I can not tell you how many times in recent weeks I've half woken up with a hand on my cats back thinking it's my babies head. Or with the head of my stuffed animal shoved up under my chin and me thinking I have a baby on my chest. My cat hates to be held or confined. It's a hold over from being stray the first 3 months of his life, he panics when confined. So he'll try to move and I'll try to scoop him closer and we'll play this tug of war for a few minutes with him trying to escape and me thinking that a baby is falling and needs to be caught and held closer. It's not until his tail goes through my clenched hand that I realize it's a cat and not a baby.
I have never actually fallen asleep with a baby on my chest or snuggled a baby in my sleep (too scared of smothering) so there's no reason why my brain should conclude that's what I'm doing when I've been snuggling cats in bed my entire life.
That's how confused baby brain can make you. It's very confusing to wake up thinking you're in the process of dropping a baby when in actuality a cat is in the process of jumping off the bed.