Has anyone ever had hypothyroidism with hashimotos but then developed sub-accute thyroiditis and became very hyperthyroid for a few months?

Yes, it is possible for someone with hypothyroidism and Hashimoto's thyroiditis to develop subacute thyroiditis and become very hyperthyroid for a few months. Subacute thyroiditis is a thyroid condition that causes inflammation of the thyroid gland, leading to a temporary overproduction of thyroid hormones. This can result in symptoms of hyperthyroidism, such as increased heart rate, anxiety, weight loss, and heat intolerance.

In someone with pre-existing hypothyroidism and Hashimoto's, subacute thyroiditis can occur as a transient phase in the natural course of the disease. Hashimoto's is an autoimmune condition in which the body's immune system mistakenly attacks the thyroid gland, leading to chronic inflammation and destruction of the thyroid tissue. In some cases, this inflammation can become more pronounced and cause a temporary overproduction of thyroid hormones, resulting in subacute thyroiditis.

The hyperthyroid phase of subacute thyroiditis typically lasts for several weeks to months, after which the inflammation usually subsides and the thyroid function returns to normal or may even swing back into hypothyroidism. Treatment for subacute thyroiditis may involve anti-inflammatory medications and beta-blockers to manage the symptoms of hyperthyroidism, but the condition often resolves on its own.

If you have hypothyroidism with Hashimoto's and experience sudden symptoms of hyperthyroidism, it is important to consult with your doctor to confirm the diagnosis and receive appropriate treatment.