At unpredictable intervals, the thyroid releases mass quantities of hormones into the body. This causes a cascade reaction in the body's hormones that regulate the metabolism - those that allow sugar to be more quickly absorbed into the cells such as adrenaline and cortisol. As a result, the heart rate and respiration both increase quickly, and the brain is quickly overwhelmed by the increase in activity. Patients will often start to panic and succumb to a flight/fight response. Blood sugar can drop dangerously low, resulting in unconsciousness and coma despite the increased production of hormones attempting to stimulate the muscles.
Thyroid storms are an emergency situation and once diagnosed (usually by measuring the level of thyroid hormones in the blood), measures must be taken to treat the underlying condition as soon as possible.
House suspected that a thyroid storm might be the cause of the patient's symptoms in Living The Dream, but Foreman worked around him to prevent House from irradiating the thyroid without confirmation.
House went to Cuddy in Insensitive to seek out an opinion about whether a patient's symptoms were caused by a thyroid storm, but Cuddy saw it for what it was - an attempt to break up her date. Surprisingly, the attempt was successful.