Based on what you describe, I would get: Thyroid Function Panel ECG Holter monitor I think you mean Xanax? This is a sedative anxiolytic used, obviously, to treat anxiety. It WILL NOT make her heart stop beating. It isn t a good long-term solution though because it is addictive and does not address the underlying problem. The vomiting I can t explain or link to tachycardia- unless she is tachycardic because she is so dehydrated from vomiting. She may have an SVT (a paroxysmal transient fast heart beat)- if so these are easily treated and carry a good prognosis.