Yes hyperthyroidism is serious because it can have effects on general health, energy, weight, growth, puberty timing, gonadal function, skin, hair, sleep, learning, body temperature, bowel function, muscle and nerve function. Also is considered an autoimmune thyroid condition called Graves disease and sometimes also associated with inflammatory thyroid eye disease. Usually first treatment is with thyroid blocking pills and then titrated according to history and followup exams as well as thyroid blood levels. If that doesnt work or if there are allergic problems with the antithyroid drugs, then surgery on the thyroid gland or radioactive iodine treatment are the next lines of treatment and all three have longterm safety data known. Id recommend asking this question directly to your thyroid doctor since its important to get an answer more specifically for your situation, labs, response etc. Also would be important to get celiac screening since celiac is also commonly associated with any kind of thyroid problem.

Yes it can become very serious if untreated. It effects your heart , wt loss , tremors, effected eyes WTH lid retraction , exopthalmos etc

It could be, especially via heart arrhythmia and unmasking heart attacks. Unnecessary anxiety, bone loss through accelerated metabolism and visual phenomena are also bothersome issues to deal with. Dr Sunil