Your immune system may be quietly sabotaging your thyroid and slowing every part of your body.
Hashimoto’s disease usually develops slowly. As the thyroid becomes more damaged, hormone levels drop and symptoms of hypothyroidism begin to appear. At first, a person might feel more tired than usual or gain weight without a clear reason. Some may not notice any symptoms for years.
In rare cases, the thyroid becomes overactive for a short time before slowing down, which can cause a brief phase of restlessness or rapid heartbeat. But as the gland weakens, the body slows down overall—often leading to fatigue, brain fog, and other common signs of an underactive thyroid.

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