The sudden onset of the pain indicates this is most likely due to an injury
to the knee. Sometimes turning suddenly while the knee is locked can cause damage to the ligaments and cartilages in the knee joint. It appears that nerves around the knee joint are also being affected. Please see a doctor as soon as possible so that the extent of the damage can be assessed. Please do not bear weight on this leg till your doctor sees you and tells you that it is safe to do so.
Hope this helps you. Best wishes.