I am 25 years old male, while dancing at a party last night I suddenly got a knee jerk in my right leg and fell down, since then I am not able to straighten my leg. I am also not able to walk as it gives me lot of pain, I cannot see aby swelling though but for any movement I get high pain ,the pain is internal and not on some specific point on my knee. Please tell me what should I do and how long it will take me to get absolutely normal so that I can run again.