The symptoms of hypothyroidism can often be subtle and easily mistaken for other conditions, but there are several key signs to look out for. Fatigue is one of the most common, as the body's metabolism slows due to a lack of thyroid hormone. This can also lead to unexplained weight gain and a feeling of constantly being cold when others around you are comfortable. Other symptoms can include dry skin, thinning hair, memory problems, and mood changes such as depression or anxiety. More severe symptoms, often seen in advanced hypothyroidism, include a slowed heart rate, hearing impairment, and in women, irregular menstrual cycles, or fertility issues.