My hamster just suddenly died!!?

My hamster just died. I played with her about 2 hours ago and she seemed fine. She was eating and drinking right. I went to check and her and it looked like she was just sleeping but when I opened the cage and called her she just layed there. I gentlly poked her to see if she was sleeping but she wasn't. She is only 10 months old. There are no marks on her or anything. Why did she die?