The pain might have occurred due to acute muscle spasm of lower back muscles.. There is also a possibility of sudden disc bulge leading to compression and inflammation of nerve root causing this severe pain.
Next Steps
I will suggest you to take complete bed rest for now. Start with Hot fomentation, Analgesic with muscle relaxant like Tab. Miofree A 4 mg twice daily for 5 to 7 days along with Rabeprazole 29 mg once daily. You can also apply local analgesic ointment over the site of pain 3 to 4 times daily
Health Tips
Avoid heavy work, avoid sitting down, avoid Indian toilet