Bas,
Definitely stop running, at least for a good while and if you start again, don't do it on a hard surface.

I had problems even walking on a hard surface when I first got PCS. This might be hard to believe, but I could feel the jarring going right to the back of my head.

If you feel that it is jarring that is because it IS jarring, and you need to stop doing it before you get the condition permanently.

Nolan gives excellent advice to try cycling. I found that even when I was at my worst, I could cycle with no jarring effects. You can even use a stationary bike. A cross-trainer seems to be OK too. Before running I would try walking for exercise. If you can do it on soft ground, even better.

Good luck,
CS