My sweet little boy had a nasty stomach bug. Five days of vomiting. He is better. Energy, appetite but he is different. He is just so irritable, screams and yells a lot, has a hair trigger. I had him checked out at the doctor to see if something else was wrong.
It is a night and day difference.
It can take weeks for someone to feel all the way better after being sick. Post illness is even a known time for temporary depression. I'd just baby him extra for a few more weeks and see if he returns to his normal self. 5 days of vomiting must have taken a lot out of him, poor little guy! I remember being extra tired for a week or two after getting well, when I was an older child.