Yeah, I have recently picked up the habit of walking daily for 30 - 60 minutes, but at the end of the day. It's quite refreshing and helpful, not to mention the physical exercise aspect. It feels good to think on the day's decisions / what happened, and think if what I am doing is what I really want or not.
>[...] by now I've seen firsthand how little practical relevance most school and university lectures had.
Yeah, I have heard this a lot. My problem lies in GPAs being used as filters, both for job applications and scholarships. It just hurts to think of the possibility that I could be passed over, not because of my actual skillset or level, but due to exam performance.
You are probably right if your goal is to work in a large conservative corporation. But for startups and medium sized companies,nobody cares.
In any case, by now I've seen firsthand how little practical relevance most school and university lectures had. So I guess the first step for you should be to stop worrying too much about doing well on any given test. Chances are, being more relaxed will also help you avoid these little concentration mistakes.