Hi obduro, I'm also 18, soon 19, and daydream all the time =).
I drink alcohol, smoke cigars (occasionally) but don't take drugs.
I avoid medicines, exactly like you. As a result I haven't been ill for more than 5 years except two colds every year (fall and spring).
Earlier I had headaches very often, but now I don't. I think the best way to prohibit them is to sleep much, and avoid stress. However, my headaches mostly were migrain.
Hope to see you more =).
BTW, where do you live?