When I was a kid growing up in a tiny town of 3,000 in East Germany, I was no stranger to a state of flow. In bad German winter weather and otherwise, I would occupy myself for hours drawing, painting, reading, writing and studying. I didn't watch much TV (and still don't) and thankfully was born before permanent distraction via mobile device became a social imperative. Philosophy classes in college were the ultimate thrill of focus and thought experiment.
A professional life in marketing I had no choice but to engage in social media, and I too succumbed to the allure and promise of quick information and pleasurable distraction, sitting at a desk for long days after brief mornings at the barn.
Every time you get on a horse, however, you better be focused. For safety's sake alone, but if your plan is to ride an FEI test or even a perfect 20 m circle, I argue that you cannot do that well unless you are in a state of flow. Of course, flow alone won't help you if your technical skills lack ("The horse can only go as well as the rider can sit." Tanya Vik), but it's pretty much impossible to consciously coordinate all the muscle movements needed to ride properly. You can remind yourself to drop your knees, engage muscle tone in your core etc, but to really ride, you have to feel yourself into the horse, you have to be fully present, you have to let go of emotions and micromanaging (i.e. fiddling with the bit).
And that's the beauty of riding: I can come to the barn with all my daily worries and fragmented Facebook brain syndrome, but once my seat bones plug into the saddle, information starts flowing my way. I start testing what kind of horse I've got today and pretty soon will get super excited when I feel a bit more engagement behind or hear the sound of my horse blowing through the nostrils, loosening the back. It becomes a state of flow where each stride builds on the next. This mediation on horseback the greatest gift, it brings sanity, focus, concentration, slowness back into a busy and hurried life, and I can't help but think that the more I can do that, the healthier I will be.
When I first started riding more than a couple of horses a day, my biggest surprise was the extent of my mental exertion. Physically I was quite able to handle it, but all those horses were new to me and I spent considerable mental energy getting to know them. That's gotten easier with knowing the horses better and also practice in feeling my way into a new horse, but the mental aspect of dressage is a huge part of its addictive powers.