This sudden pain might have occurred due to acute muscle spasm in lower back muscles.. Was there any injury or jerk..
Posture change may occur due to sudden spasm in lower back muscles on one side..
Next Steps
You can take complete bed rest for now. If pain is severe, take analgesic with muscle relaxant tablet, apply analgesic ointment locally, start hot fomentation
Health Tips
Avoid heavy work, avoid sitting down, avoid Indian toilet, avoid forward bending...