The thing about Relativity and its decay/delta settings is that they tend to apply across the board to all sims. So a more common symptom of settings needing to be readjusted would be that everyone in town, active and inactive, is getting tired too early in the day. Or no one ever being tired at bedtime or everyone all around you waking up at 3am fully rested.
A few threshold questions, but you may have already thought of these things.
-- Is this sim getting out of bed less than fully rested and lacking the fully rested moodlet whereas the others are getting something closer to a full night's sleep with totally restored energy? If he isn't staying up all hours of the night, maybe he needs a better quality bed.
-- Does this sim's day start significantly earlier than everyone else's?
-- Is this sim routinely engaging in any activities that drain energy faster, such as athletics (among other things), whereas the others are not?
-- Why can't he sleep in class like the rest of us did when we were in school? (although effective, this one isn't meant to be serious as there will be repercussions like detention if it becomes a habit)