Exercise is a funny thing. It's hard and it's draining while you do it. However, the body and the mind starts to like it more the more you do it.
During this summer I've been exercising, a lot. At least according to my standards. In the month of July alone I had clocked in 59 hours of gym, cycling, running, walking, and disc golf. In my standards that's quite a lot. Yes, it includes commutes with my bike and so on, but still it's averaging almost 2 hours a day. Some days have been harder and some others have been less hard. I am using an Apple Watch to track my activity, and also in June, I averaged about 1400 kcal per day of active movement. That is on top of the 2200 kcal of BMR that I have.
From all of this I notice that my mind is calm. It's calmer that it usually is and I can just let go of things. I notice that after a day of being active I can just catch myself laying on the couch drifting away in thoughts about random things. On days I have not been exercising I don't have this, and instead I am over-analysing things running different scenarios in my head.
I've read this interesting article about energy consumption and how that is related to the activity level of humans. The point in the article is that there might be a hard limit on how many calories a human can burn in a day. And when ultra endurance athletes head on day-long events, the other calorie-costly "processes" of the human slow down. These can be for example the stress responses and high alert modes. In other words, by exercising more, you will have less energy to put into worrying and being stressed. There just isn't enough left for that.
I think that I've noticed that in myself in the past few months. And I love it.