Many of you out there know some of the common symptoms of low thyroid function, such as fatigue, weight gain, constipation, headaches, hair loss, depression, and cold intolerance.  I've also explained to many of you how the thyroid functions in the body.  Think of this gland as your engine.  If your engine is too 'revved up' (i.e., hyperthyroid), bodily functions will be overactive, such a s overactive nerves causing jitters, shakiness, anxiety, fast heart rate, palpitations, and high blood pressure. Bowels may be overactive causing excessive bowel movements or loose stools.  Temperature gets higher, metabolism gets faster, and so on.  If your engine slows down (i.e., hypothyroid), bodily functions slow down.  Energy gets lower, brain function gets slower, mood is lower, bowels are slower, pain threshold is lower, temperature is lower, metabolism is slower, and so on.  It's also important to note that some symptoms can occur on either end of the spectrum.  For instance, you can be tired if thyroid function is lo w or high.  You can lose weight or gain weight on both ends of the spectrum.  You can be shedding hair when thyroid is under-active or overactive.  And also noteworthy: 1) symptoms can vary, such as you may have normal bowel function, but have other symptoms of low thyroid, and 2) having normal thyroid labs does NOT mean that your thyroid is functioning adequately.  (You can read about that here.)  Moreover, there are many factors that affect how well your thyroid functions at the cellular level, including diet, gut health, stress, toxins, vitamin deficiencies, and imbalance of other hormones in the body.