1. You may want to check the side effects of your meds. There are AED meds that have the side effect of wieght gain.

2. Next time you see your Epileptologist or Neurologist , make sure they have your medication levels. If the levels are low your Dr. May have to either increase the meds you’re on or change to a different brand/generic AED medication.

Check with those first .

You can start with finding out the side effects of your medication. Some do have side effects of weight gain. And some make us feel fatigue to the point that we don't exercise. I am trying to fight the latter. Diet can play a role in some seizures also. For some, caffeine will produce seizures even if you take your meds. That's why i can't have certain beverages like coffee, soda and chocolate. All have caffeine.

Being overweight does tend to cause diseases in the body but I don't think being overweight causes seizures .
I'm trying to get to a healthy BMI because i have mild sleep apnea and I was advised to lose weight by my doctor if losing weight will cure it I'm all for it .

I don't know about weight gain itself but in my experience, the things that cause weight gain, like sugars, caffeine, poor sleep habits, lack of water etc., have also tended to be triggers for me.