I did too a few years back, and it clouds the brain no-doubt. It got to the point where something had to be done, and so I set everything aside and dedicated 6 months to figuring out how to fix it.

Read this book: Spark: The Revolutionary New Science of Exercise and the Brain by John Ratey (http://en.wikipedia.org/wiki/John_Ratey), the professor of psychiatry at Harvard Medical School.

I have posted on the effects of sprints several times over the years so rather than repost again, here's a link to the threads: https://hn.algolia.com/?sort=byPopularity&prefix&page=0&date...

Running sprints were key, but inflammation due to diet was part of it too (a latent issue not widely discussed, but a factor more common than you might think). I solved that by eliminating certain foods one by one that are known to cause inflammation. Peanuts were one, and eliminating aspartame (diet coke) had a noticeable effect within just a few days (I verified it wasn't the caffeine by adding back tea and coffee, and those had no noticeable effect).

Here's some links to the original Harvard and USG research findings on the issues with aspartame and artificial sweeteners/flavors in general, like why it's banned it baby food: https://news.ycombinator.com/item?id=6703802