It's unlikely to work. It is more likely to leave you with permanent brain damage, even in incredibly high doses. There are accounts of people surviving several grams. I know you don't care about the pain, but it would really be the most agonizing experience. Physical side effects aside, it's not hallucinations from "tripping" like you trip on psychedelics, it's actually just psychosis and permanent brain damage being dealt. I am so sorry you are suffering so much. Please do not overdose on benadryl, you will live to regret that so much. I know it doesn't mean a lot, but I'm sending peace and love, and I hope you reconsider this method.