SIDE EFFECTS TO EXPECT WHEN MY DOCTOR HAD TO IMMEDIATELY STOP TAKING DILANTIN

I was recently diagnosed with Breast Cancer that had mestasticized to the brain. They put me on Dilantin immediatedly and then I went through 20 treatments of full brain radiation. However, the last day of radiation I developed a measel like rash on my arms and under torso so they immediately stopped the dilantin. I know they suggest you taper those out, but I had to abruptly stop them. I was wondering what possible side effects you experience by having to stop taking them abruptly versus tapering them out of your system. Also how long do these effects last?

Sandy Stratton