Thank you for the advice, peeps! Yesterday I came home from work and saw he was not so active and has been lingering at his seed cups, then I took a closer look to only find he has finished up all the seeds. So I fed him some millet and strawberry and he devoured the millet.
After the meal, he was hyper at night and playing and jumping around his toys and refusing to go to bed. Then he quiet down by 930PM and I able to cover his cage with blanket. Hopefully he got better. Will keep monitoring.