Interesting thread. I'll add my anecdote. For me, the difference is very distinctive.
From physical exertion, I get a flu-like feeling. When I was mild I noticed I got it more from endurance-type sports than strength training.
From cognitive exertion, I get a different "wired" feeling and tingling sensation in the joints. Relevant example is concentrating long and hard on something, like computer work, especially when I am very invested and take few breaks. I also get it from drawing or writing, but these involve more muscle activity.