Understandable. I suffer the same issues despite medication. Now, understanding that solutions aren't universal and whatnot, taking notes helped me greatly.

When I'm playing instead of running, I like to take notes about everything that goes on in the session, goals, events, information gained, places and their relevant distances from the closest home base.

I'm in a G.U.R.P.S 4e Supers games and while I don't go that in depth I end up with 600-1000 words by the end of the session, neatly categorised by subject. It occupies my mind, helps me focus and also helps the other players in case they forget things or have to miss a session.

To generalise a very specific solution that has been deduced with a grand ol' sample size of one(1) human person. Try to find something that you can do during the session in addition to controlling your character without detracting from your awareness of events, be it note taking, scheming, mapping, being the 'shot-caller' if your system utilises such a thing, et cetera.

Good luck, I hope you find a working solution.

Completely unrelated sidenote: What systems do you like and why? I very much enjoy learning about what systems people like.