Garfield is actually dieing of starvation, and just imagining Jon and Odie. There was a reference to this in a Halloween themed comic. Garfield woke up in a condemned and abandoned house. He calls out for Odie and Jon, but there is no answer. He then wills the illusion back on himself, and continues his delusions about his 'family'.
Now go back and highlight the blank space before the above comic, right below the title.
Read the last panel of the comic.
Have a good day.