I've never heard anyone report that diabetes made their cat angry or violent, paula. i've been on FDMB for almost 4 years and the only cat that became violent was Morgaine, who developed dementia. She's also the only cat I've heard of who developed dementia. I don't think that's what's happened to Michael.
Who knows what happened yesterday, but I would try to put it out of my mind and concentrate on today. Looks like he's thinking about clearing the bounce tonight.
If it happens again, i think getting his thyroid levels checked and an overall vet visit might be a good idea.