Don't have any burden, think about it, the road ahead is long, there are many opportunities, so young, what can you afford to lose? Big deal, start over. So eat when you should eat, sleep when you should sleep, play and study when you should play, but don't be burdened. Relax, everything will be fine.
You said you were a cheerful child. I think you still have a lot of ideas, which is not bad, but you are too tired to think too much. Let go, especially don't think about words like sub-health. It was the doctor's idea to scare people. If you feel unwell, see a doctor. If there is no discomfort, it is healthy.