This is probably going to sound crazy but..

[Jellyfish]

Sounds like it could be teething. Any bumps on the gums?

[*LittleMissSummer*]

My DD woke up screaming hysterically the other night took us a while to calm her down. And she does whimper in her sleep sometimes.

I'm very interested in knowing whats happening. I just thought it was a bad dream.

[Enchanted]

Both my kids did that and I have always thought it was a bad dream too.

It didn't last long though, I always thought they were dreaming about their boobs being taken away

[UntoldAngel]

P cries at times and I was told it is just them moving through the sleep states.. I don't know if it's true, but when he screams like someone has hurt him it can't be a good thing

[Asparagus and Lemons]

It is horrible as she gets really upset. sometimes she does randomly whimper in her sleep and I understand that to be the rem stage of her sleep. But not this. its too upsetting!
Yes there are lumps on her gums. But why would it hurt while she is sleeping?