Heather,
It is unclear what symptoms and diagnosis you are being treated for, with a combination of Zoloft, Xanax, and Cytomel (Liothyronine). Any of these three medications may be associated with the disorientation, lightheadedness, dizziness, and derealization that you describe. I urge you to discuss your concerns further with your treating physician/psychiatrist.
Heather,
It would also be important to have a thorough physical examination, to rule out medical and/or neurological causes of your symptoms.