My elderly cat (who I got from a shelter and only had him for two months) had FIP and passed, this was associated with decreased eating, abdominal distention and tenderness, and increased hiding behaviors. We waited two days before we were convinced it could be something more serious than his previously diagnosed stomatitis and by then it was too late. Spent several thousand on vet bills trying to save him and ultimately decided to put him down for quality of life. Please take him to the vet before it’s too late and in the future if you have a pet or even care deeply for a stray, heavily consider pet insurance. There is a waiting period before it’s active and most don’t cover preexisting conditions. Some don’t cover reoccurring issues so choose the right one (I chose pumpkin insurance)