Hyperthyroidism: excessive thyroid gland activity, marked by increased metabolic rate, goiter, and disturbances in the autonomic nervous system and in creatine metabolism; sometimes used to refer to Graves' disease.

This metabolic imbalance results from Excessive thyroid Hormone.  The most common form of hyperthyroidism is Graves' disease, which increases T 4 production, enlarges the thyroid gland (goiter), and causes multisystemic changes.  An acute exacerbation of hyperthyroidism is called thyrotoxicosis, and is a medical emergency that may lead to cardiac failure.

Cause:  Believe to be an autoimmune disease.  Antibodies to thyroglobulin or to thyroid microsomes occur in most patients with this disorder.

Symptoms:

Enlarged thyroid
Nervousness
Heat intolerance
Weight loss (despite increased appetite)
Sweating
Diarrhea
Tremor
Palpitation
Exophthalmos (abnormal protrusion of the eye)

Thyrotoxicosis symptoms:  may include - irritability, hypertension, tachycardia, vomiting, temperature up to 106 degrees F., delirium, and coma

Other sings and symptoms include:

CNS:  difficulty concentrating, excitability, nervousness, fine tremor, shaky handwriting, clumsiness, and mood swings.

Cardiovascular system:  tachycardia, full - bounding pulse, wide pulse pressure, increased cardiac output and blood volume, cardiomegaly, paroxysmal supraventricular tachycardia and atrial fibrillation (more so in elderly patients), 

Eyes:  exophthalmos, inflammation of conjunctivae, corneas, or eye muscles; increased tearing, lid retraction, the perception of two images of a single object (diplopia)

GI system:  increased appetite, but occasional anorexia, increased defecation, soft stools or, with severe disease - diarrhea, and liver enlargement..

Musculoskeletal system:  weakness, fatigue, and muscle atrophy.  generalized or localized paralysis associated with hypokalemia; soft tissue swelling

Reproductive system:  in females - oligomenorrhea (abnormal infrequent menstrual cycle) or amenorrhea (absent or abnormal stoppage of menstrual cycle); decreased fertility; higher incidence of spontaneous abortions. 
In males:  gynecomastia (excessive development of the male mammary glands, even to the functional state.)
Both sexes:  diminished libido

Respiratory system:  dyspnea (difficulty breathing) on exertion and at rest rest

Skin, hair, and nails:  smooth, warm, paper thin, flashed skin;  accentuated hair follicles; raised red patches of skin that are itchy and sometimes painful, with occasional nodule formation; fine, soft hair: premature graying and increased hair loss in both sexes; friable nails and distal nail separated from the bed (onycholysis)

Treatment:

Treatment depends on the size of the goiter, the causes, the patient's age and parity, and how long surgery (if needed) will be delayed.

Antithyroid drugs
I, beta-adrenergic blockers
Surgery (if needed)