In college, my astute psychiatrist sent me to learn relaxation techniques.
I had panic attacks during the relaxation exercises. So we stopped.
This lovely man, Ron Gatsik (I mention his name because he was so kind and helpful, and has since passed away) didn't know that I had ADHD; adult ADHD was unknown at the time. He knew that I think too much. And he was pragmatic. The problem with the relaxation exercises, I now can understand, is that the mental chatter just kept going, and I would fight to keep the noise down. I would try to quiet my mind. But I could not. So the chatter that was just tiresome would become irksome and disturbing; I struggled with myself; I felt bad because I couldn't shut up inside; I panicked because I was getting agitated and this was so not supposed to be the result.
That's why I tend to say inattentive folk aren't so much always lacking hyperactivity, it's just that the hyperactivity is internal, mental.
Nowadays I know not to fight for internal quiet. Frankly, the TV works a lot better than the relaxation exercises do on a bad day; and if I try to chill out the internal chatter and it doesn't work, I can just walk away from trying, instead of fighting it.