Underactive thyroid symptoms. Any time that the thyroid is underactive it is called hypothyroidism because the gland that is located in the front of the neck is not secreting enough of the thyroid hormones. There will be a decrease in metabolism. A person will feel very sluggish, very tired. They may have weight gain, may even be obese. They'll have cold sensitivity. They will be very chilly and cold. Their skin will be dry and pale. Their muscles will tend to be very sore. They may present with depression with a decreased respiratory rate. They might have constipation, have trouble concentrating with memory loss. Also their menstrual cycles may be having problems. The gland itself could be swollen which is in the front of the neck so when a person has hypothyroidism or underactive thyroid then they are going to present with most of these symptoms.