Hello, I am a very active 18 year old girl, I lift and go to the gym a lot. Recently I was sitting in a crossleg position and after a while my knee began to hurt. I do not remember specifically injuring it, or overusing it at the gym. I sleep with my knee bent and have been awaken at night by the pain in my bent knee. When I straighten my knee to relieve the pain I feel a slight pop. I can run and walk without pain. It seems to hurt when my knee is bent and at rest. What could this be? How do I treat it?