If you have tinnitus, I'd stay as far away from ketamine as possible. This also goes for any form of stimulant, including caffeine and nicotine. In my admittedly limited experience, any substance that significantly raises blood pressure and/or contracts blood vessels will aggravate tinnitus symptoms, if not make them permanently worse. Every case is different, of course, but I think this aspect is well worth discussing with your ENT. Best wishes to you.