Detox illness, is it a thing?

I have been a regular smoker for a decade now, I use it for my ADHD, to help me focus and get stuff done. It really helps. However, I regularly travel for work to places where weed is illegal. I I am recognizing a pattern, when I don’t smoke for a week, or so, I get sick. Not just a little cough or detox sweat, but flu like. It’s happened 4 of my last 6 trips. Does this happen to anyone else? Or is it just a coincidence?