My cat is high. i think.?

he's old. like 9 or 10. lately he's been just laying around acting emo as frick. i woke up this morining, and he's chasing invisible mice around my brothers new spiderman extedable couch or w/e. . . now he's just eating. idk what to do, he was running around like someone fed him crack-cookies. idk what to do. yesterday i was hollding him, and he's like.... really really hard in the stomach like a huge knot or something. Any help?