seizures
"I had surgery for a benign brain tumor over 8 yrs. ago; Gamma Knife radiation surgery 3 yrs. ago. The Gamma Knife surgery left me with scar tissue that caused me to have my first partial seizure. This required me to remain on seizure medication, levetiracetam. 
To prevent recurrent seizures, I was on a dose of 1,000 mg./ 2x's day. I was on this dosage for over 2 yrs. No seizures, but side effects crept up slowly: bad memory loss, difficulty finding words, fatigue, weight gain. Then, the intolerable ones: deep depression, mood swings, crazy flip-out anger. It just kept getting worse, until I couldn't wait to get off of it! My doctor called it the "Keppra Rage". I guess this is well- known side effect that I could not tolerate."