Playpennies

My almost 3 year old daughter has been waking up in the middle of the night screaming and crying. She has always been a great sleeper but within the last few months this keeps happening and she won't go back to sleep unless I put her to bed with me. I'm not sure what to do.I can't think of anything that's happened to frighten her so badly. Any thoughts? It's so bad I am dreading bed time myself!