Hashimoto's is an autoimmune dissease. What this means is that your immune system is producing 'antibodies' which attack the thyroid gland. As a result of this, the cells of the thyroid gland are either; killed (and nolonger produce hormone), or damaged (causing overactivity).
Thyroid hormone controls metabolism. Metabolism is the sum of chemical reactions that keep everything balanced inside your body. So, if your thyroid is underactive, you have a slow metabolism, which can cause a person to; gain weight(or have difficulty controlling it), slowed heart rate, have high cholesterol, have muscle weakness/aching/fatigue, hair loss, cold intollerance, and many other symptoms.
However if your thyroid becomes overactive, you will have an increased metabolism causing symptoms like; increased heart rate, weight loss, heat intollerance, muscle weakness, fatigue, restlessness, anxiety etc.
Generally, I think emotional implications are simply caused by the reaction a person naturally has to feeling so totally off-ballance, but thyroid dissorders can often impare a person's concentration and mental ability, which can be very distressing.
That's my limited understanding of it, I hope it helps