The symptom isn't due to any heart issue as inspiration should cause chest pain or any chest discomfort. However, that doesn't rule out your having a heart issue concomitant with another medical concern. Is your heart rate normal at rest? Do you know your blood pressure? I'm not sure how a thyroid gland removed effects the body system, and whether or not that can be the underlying cause, but the matter should be discussed with your health care provider.
Thank you for your question, and if you have any other questions or comments you are welcome to respond. Take care,
Ken