Yes, the good news is that sinus tachycardia is generally benign (not harmful). The bad news is that there's no known cure for dysautonomia. However, there are many many treatments to address the various symptoms of dysautonomia. If your current cardiologist isn't experienced in this field of medicine, you may want to seek out an electrophysiologist ("EP Cardio") to treat your condition. The other option is a neurologist who treats dysautonomia, but considering yours is related to your heart surgery, you might have better luck with an EP Cardio.
Depending on the cause of the dizziness and whether it is vertigo or light-headedness, a neurologist should be able to address those symptoms for you. Doctors in the field of "neuro-otology" or "otoneurology" (brain and ear conditions) may specialize in treating dizziness, so it may be helpful to look for a practitioner in that subspecialty specifically, though any neurologist *can* treat dizziness.
I'm including a link to our health page on dysautonomia treatments for you. Please note that no one dysautonomia patient will have all of these symptoms, so only some of these treatments would be appropriate for you. At least by studying up on your options, you can have a more informed discussion with your doctors about what is right for you.
Cheers, H.
http://www.medhelp.org/tags/health_page/24603/Dysautonomia/Dysautonomia-Treatments?hp_id=171