One thing is for sure: ADDers can not easily “relax” in typical ways ( e.g. reading a long book that is not a mystery). Since they can readily become fidgety and distracted, they would do better to engage in an activity with high stimulation( e.g. running or walking on a treadmill or watching an action movie).
Another way some ADDers seek stimulation is to worry and hyperfocus on physical symptoms. They are often not aware that they are hypochondriacs, and they run to doctors all the time ( That is not to say that symptoms should not be checked out).
I recommend that an ADDer, when unstructured or bored, needs to have at hand a variety of stimulating activities to engage in that are not dangerous. In fact ADDers do better when there is too much to do, rather than nothing to do.