Far be it for me to tell anyone what maximallly happy existence is. I'm sure AI with full understanding of human physiology can figure that out.

I would venture to guess that it would not include constant stream of events the person undergoing the simulation would write on a paper under the title happy stuff, but some minor setbacks might be included for perspective, maybe even a big event like cancer which the person under simulation would manage to overcome?

Or maybe it's the person under simulation sitting in empty white space while the AI maximally stimulates the pleasure centers of the brain until heat death of the universe.