My Husband Has Had A Pain In His Lower Right

My husband has had a pain in his lower right side of abdomen that subsided but came back and is in abdomen, going towards his back too. He is now on his way to the hospital in an ambulance because he is in such pain. Threw up 2 times last night. Unlike him to not be able to tolerate pain or take day off from work, which he did. He has not eaten much today, just some mashed potatoes this morning, but pain is very bad now. What are the possible causes?