Likewise, I actually love that feeling when you’re running and after a certain point of exertion your mind goes blank - I find it so rare to have a blank mind in day to day life. Similar feeling to when you’re skiing/snowboarding and really in the zone, though not as intense.
I do sometimes find I come up with good ideas for work/whatever when running, so it can be a good way to ponder things like that and I’ll sometimes record a short voice memo on my Apple Watch otherwise I forget what I thought of. But after 20 minutes or so I find my mind kind of defaults to blank and I like that!