How'd That Happen?

Cate has a very mysterious injury. Last night, she was laying in our bed watching Dora when she started screaming hysterically. We found her laying on the ground with a huge chunk of hair missing from her head...which we later found on the floor next to the bed. There were no other markings or bruises on her, so we have no idea what happened. She's sporting a comb-over to hide the missing hair and I'm hoping it grows back fast...it took her nearly two years to grow it!!!