Hi, dear
I have gone through your question.
I can understand your concern.
Rapip heart beats is a sign of hyperthyroidism, but for the right diagnose my advice is to see an
endocrinologist because in my opinion ,you need to repeat the thyroid tests(TSH,T4,T3) to understand the actual thyroid function and a thyroid ultrasound to see the nodule characteristics.If there are ultrasound features of thyroid malignancy,your doctor might perform a fine-
needle aspiration biopsy of the suspicious nodule.
For the diagnose of Hashimoto's Thyroiditis your doctor might ask Anti-thyroid antibodies (ATA) tests, such as
thyroid peroxidase antibody test and the anti-thyroglobulin antibody test.This test is commonly used to confirm or exclude Hashimoto's thyroiditis as the reason for hypothyroidism.(if the results show
low thyroid function.)
After all these investigations your doctor will be able to reach the definitive diagnose and you can have an explanation of your symptoms.
Hope I have answered your question. If you have any further questions I will be happy to help.
Wish you good health.