What do I do with my kitten?

My kitten the other day hollered for no reason, and I think she was just playing too rough with the other kitten. When I found her, she wasn't acting the way she usually does which is hyper and all over the place. She was just lying, not moving and now for the past couple days she has no will power to do anything, she just lies down in an area all day and just seems to have no stamina. I don't know what to do with her!!! Any advice?