Thyroid symptoms are plentiful, but non-specific, meaning they can be due to many different causes. However, the more symptoms that are present, the more likely it is to have thyroid dysfunction. Interestingly, some symptoms are present in both overactive and underactive thyroid, such as fatigue and hair loss. Many of the other symptoms are opposite, as one would expect. Please see the images below that describe symptoms of hypothyroidism and hyperthyroidism. Then see the related article regarding thyroid hormone levels.