The thyroid is a small gland located in your neck. When it does not produce enough thyroid hormone, you may suffer from hypothyroidism, when it produce more that would be hyperthyroidism. The symptoms of hypothyroidism can be vague and resemble other conditions, but some common signs include swelling of the thyroid gland (goiter), fatigue and weakness. Likewise hyperthyroidism will make you heat intolerant, unable to sleep, muscle weakness, etc.
Do you have any issues with your thyroid?