I would definitely try Keppra. It has essentially "cured" many HPPD sufferers of their symptoms. I tried it for about 10 days but it eventually made my depression much worse, but that's just how my body reacted to it, others have had much better success. I currently take a benzo called Lorazepam or Ativan, and i know you said you didnt want to start benzos but if the keppra fails, you should ask your doc about ativan or even klonopin. I am also on a liquid form of lexapro in which i take 1 mL (1 mg) per day and will start to increase by 2 mL everyweek starting this next week. My doc has told me it should help with my social anxiety and depression. The ativan really helps me at school and i am waiting for the Lexapro positive affects to eventually kick in. I hope everything goes well for you, stay hopeful, no matter how hard is to do, and a silver lining will come.
Richard