How do i tell my parents something is wrong with me?

well im 18 i have bad mood swings some days im sad other days im mad or happy or in a irritable mood i also cut and have a eating problem. i know its bad to cut that's why i want to get help .the thing is i been keeping this a Secret for 5 years and im not good at opening up and im scared to tell my parents i don't know how they are going to react how do i get the courage to tell them?