The feelings you described are consistent with a diagnosis of social anxiety. It can be debilitating — something you know only too well. You wrote an articulate and organized letter which tells me you can probably do fine with graduate work if you could only get your anxiety under control.
I do understand why you are afraid to go to a doctor. Most people with social anxiety are afraid of interactions with just about everybody and a doctor is no exception. But doctors are exactly who you need to see. In fact, you need to see 3 different helpers to get the help you need. Please have some optimism. Most professionals are just that — professional. They don’t want to judge you. They just want to help you.
First, if you haven’t had a complete medical check up in awhile, do get one. You want to be sure that there isn’t something medical going on as well as the anxiety. Once that’s been done, you need to see a psychiatrist for some medication to settle things down enough that you can start to use some therapy. Right now, you are just too, too anxious. Finally, you need to make an appointment with a cognitive-behavioral therapist to learn how to cope with social situations, including classes, and to manage your intense feelings. There is nothing at all wrong with being a bit anxious. Everyone is. But your anxiety is so intense that it is getting in the way of your life. You need to learn some skills for toning it down — and for feeling more in control.
While waiting for appointments, I do suggest you get a copy of Feeling Good by Dr. David Burns. Read it carefully. It will give your therapy a jump start.
You have suffered in isolation for far, far too long. You deserve better. Please, let the helpers do their job and do your part. You can get much better.
I wish you well.