Your thyroid gland is situated in your neck. It produces a hormone called thyroxine. This hormone is important for your metabolism and has an effect on multiple organ systems. If your gland becomes overactive it means that it is producing too much of this hormone and this increases your metabolic rate. This is why symptoms may include palpitations, anxiety, flushes, weight loss and insomnia (difficulty sleeping) and why treatment of your overactive thyroid is so important.