Kewky,
I sympathize with your fear. I've had a lot of fear myself in life and a lot of trouble performing up to the level of what I was told I was capable of. I've had "loads of potential" that never seemed to work out.
For what it is worth, I'd like to give some small bits of advice to think about.
1. Allow yourself to deal with just One Day At A Time! When you worry about your whole future at once you can drive yourself into the ground and have no energy left for the actual day.
2. Stop being mean to yourself. It won't get you anywhere good.
3. You don't have to choose a profession to "show them what you have". It is a bad idea because most people are not looking as close as you think. You need to pick a career that interests you that is compatible with your traits, abilities, energy levels and financial needs.
There is a way to deal with your problems. You will find some help. You can choose to feel hopeful instead of feeling doomed. You are not doomed even if you have some definite problems.
I am speaking out of experience. I too have had several diagnosis. Mylife has not turned out like I would have liked. However, I am doing better than I could have thought 5 years ago. You are NOT hopeless, you will find a way through this. Choose all the positives you can, you do have the power of choice more than you think.
Good Luck,
Leslie