I could have written the OP. And this constant inability to relax is something I've been warned could become a health issue (including by my doc, who recommended yoga). Yet, I come across pretty calm to most. The racing thoughts cause considerable impatience with people because I get frustrated when something is not being addressed/ handled properly and I find I have to reason with myself and slow it down.
It's one of the ways my INTJ and I are (too) similar. Forget quiet meditation. That doesn't help me get out of my head, which is key. We both find vigorous exercise more helpful.
Ti (43); Ne (41.8); Te (33.7); Fi (30.5); Ni (27.5); Se (24.7); Si (21.5); Fe (17.3)
The More You Know the Less You Need. - Aboriginal Saying