They would be relieved because there is a reason for what is going on with you. It is not your fault. You can get help. You already said your mom is getting angry and so are your teachers. You want to be motivated but you just can't be. Do you want them all to think falsely that you are just lazy and don't care. Do you want to get punished for something that your really don't have any control over. How is that fair to yourself.

If you tell your parents and they bring you to a psychologist that is a good thing. They can figure out how to help you. No your teachers don't have to know a thing. Everything between you and a psychologist is confidential. Your parents don't have to be in on the session.

Find a way to get the help you need. Why should you continue to suffer all by yourself. You said it is killing your grades and the things you care about. It will be hard and you will run into people who don't understand......but you know what screw them, this is about you and your health and that is what is most important.