Thanks for the feedback!
Have you directly experienced epilepsy problems while playing? Do you think there are better way to notify the player that the SlowMo is enabled? Was it the effect on the border of the screen? Do you think that by making the effect more subtle it would be better?
I'm asking because sure, I can definitely put a warning, but if people are experiencing epilepsy attacks that warning doesn't really fix the problem: I would rather improve the UI and solve the problem at its root.