RAI treatment for hyperthyroid disease

hello, i m so glad to have found this site. i have been unsuccessful in getting support and/or answers. a week ago i had RAI treatment for my hyperthyroid. i am feeling a lot of dread regarding the possibility of hypothyroidism. how will i know when it begins? i dont want it to become severe before i realize it. this happened to my sister and it was very frightening. can anyone give me some idea of what to watch for? i would appreciate any information or help.

sincerely,

diler