So today i got up fast and something in my knee felt like it moved out of place and moved back and now its sore. its happened before. what is it?

Could be cartilage: Many things inside the knee can do this. We call this internal derangement of the knee. Loose cartilage form a previous injury or a inside the joint particle which we call a joint mouse could be causing this. Speak with your physician about what the possibilities could be. You may need imaging including X-rays or MRI or even arthroscopy for the diagnosis