allergic reaction...
My Brutus woke up from a nap suddenly and started having an allergic reaction. He was scratching at his left ear something fierce, panting, frothing. I cleaned his ears out thinking they were dirty and bothering him. That didn't help. So when I looked him in his face, I saw a blister looking mark at the corner of his right eye. And his right eye was almost swollen shut, he was covered in hives, and his left eye was beginning to swell. The only thing I could think of was a spider or bug bite of some kind. We were inside, hadn't eaten recently, quiet. I called the vet and was told to give him the Benadryl and only bring him in if he develops difficulty breathing. I continued to give him the Benadryl every 8 hours for the next 24 hours until all the swelling in his eyes had gone down. It was his first allergic reaction, mine too! That night I stayed awake for hours just listening to him breath. Scared the daylights out of both of us. Sometimes though it's not always food related. I'm pretty sure that little blister next to his eye was some sort of bite. Good luck!