There is a possibility of lower back muscle spasm while getting up from sitting position. Sometimes, there is a possibility of some ligament tear inside vertebra leading to disc prolapse.
Next Steps
He can start with complete bed rest for few days, start hot fomentation 3 to 4 times daily, take analgesic with muscle relaxant tablet, apply analgesic ointment locally. If not relieved, he may require some investigations like X ray or MRI.
Health Tips
Avoid heavy work, avoid sitting down, avoid Indian toilet, avoid forward bending..