Overactive thyroid diagnosis?

or the past few weeks i've been having a fast heartbeat so i went to my dr. and he did some tests and told me i have an overactive thyroid and has referred me to an endocrinologist. i'm scared...does anyone know what i can expect there? i'm not going for a week...i don't really know anthing about this disease or what these drs do. i'm 20 years old. i don't want to be on medicine for the rest ofmy life