Your thyroid produces thyroid hormones, which control all of the metabolic activity in all of your cells. It's important that your thyroid is functioning properly. Many people may not even know they're suffering from hypothyroidism because there are so many different symptoms. The classic symptoms of low thyroid are fatigue, weight gain, being prone to depression and anxiety, joint pain, and water retention. It can be caused by stress, pregnancy, Hashimoto's Thyroiditis, nutrients (or lack thereof) and some medications. If you're concerned that your thyroid may not be functioning the way it should, you should see your doctor and get tested.