Hashimoto's thyroiditis since 1995. Had thyrotoxicosis several times. This time severe palpitations are there but tests normal. Tsh 0.98 & ft4, 1.55?

Not thyroid. Thyroid fxn is normal. Please see your doctor to address why you're having persistent palpitations.
Other related causes. It is possible that other conditions such as coronary artery disease and related but new autoimmune dysfunction can occur. You may need you heart checked. A good option is multifunction cardiogram...http://en.m.wikipedia.org/wiki/multifunction_cardiogram.