Slipping of knee is sign of knee ligament injury. You will need detailed evaluation. Depending on grade of injury surgery or conservative (non surgical) treatment will be recommended.
Next Steps
Kindly visit orthopaedic doctor for further evaluation and grade of injury. MRI scan will be helpful.
Health Tips
Use ice pack for pain reduction. Try to walk using a cane in opposite side and if possible a knee brace will help protect your joint.