Fears/Nightmares

I'm not sure if they are nightmares but Libby has started talking...er screaming...in her sleep. It started a few weeks ago and now seems to be a regular thing of once or twice a week. I'm not sure what is causing it but there is nothing like being woken up by your child screaming for you, you hurry to get up (or you get up as fast as you can while 25 weeks pregnant), and get inside her room to find her completely asleep with little tears coming down her face. It breaks my heart. I don't know what is causing this and all I can do is rub her arm/back, tuck her in completely, and softly tell her she's ok. Is this normal? It just is so hard to watch and I am a fixer. I have to fix this somehow but I don't know where to start. I thought it might be from letting her see movies like Bolt or Finding Nemo recently but that was weeks ago. If that did cause it, wouldn't it be out of her system by now? I dread the hours between 1-4AM because that is when she always has them. =(