What are common symptoms of a sluggish thyroid?

Many. Weight gain, tiredness, dry skin, coarsening of hair, fatigue, depression, constipation, swelling in the legs, cold intolerance, mental slowness, menstrural irregularities, slow pulse, and many more. (is there anything left?).
Out of gas. Some of the symptoms are fatigue, constipation, intolerance to cold. Dry skin/hair are also common. Some may also feel puffy depending on how hypothyroid they are.