hi dexxy I've also been on antidepressants before , and quit cold turkey. I thought, "oh I'm doing so well now, I don't need these pills anymore." so I just stopped. soon after, I was swept up in my worst episode yet. it went for months, and once it finally ended, I became so manic I lost what few friends I had. one thing my therapist told me was to consider how bad your symptoms were compared to the side effects you're experiencing. if you stop your meds, you'll probably lose the stability you've gained. that being said, I don't know much about tachycardia, or how serious it might be. if it's really concerning to you, you should definitely contact your doctor and see what they say.