Hypothyroidism is a disorder where your thyroid is not manufacturing enough of thyroid hormones, which may occur because of the thyroid gland being compromised. Some of the symptoms of hypothyroidism include sudden or rapid weight gain with no discerning shift in food consumption or exercise, being tired all the time, being irritated, and being constipated.
Hashimoto's thyroiditis is a disorder where the immune system attacks the thyroid gland. This may occur without any corresponding symptoms. Hashimoto's patients will not generate the same antibodies, while hypothyroidism does not present the same, and the thyroid antibodies involved are called anti-thyroglobulin.