You sleep eight hours a night, but you still feel sluggish. You haven't changed your diet, but you're gaining weight. To top it off, you're feeling achy and depressed. It's easy to blame these symptoms on a busy lifestyle or advancing age, but for millions of people — especially women — your thyroid is the culprit. Hypothyroidism develops when your thyroid isn't producing enough thyroid hormone. In this section, you'll learn all about this type of thyroid disease — from being diagnosed to seeking treatment.