How about I did something absolutely horrible today? I can't even tell you the whole details.
Can you give me an idea on what you did that was so horrible?
Well, I committed a horrible act today. I have been so ashamed of myself.
It's unfortunate that you did something horrible, but taking responsibility for it is a good thing. I think you should apologize to whoever you hurt and try to repair any damage you caused, because that's the right thing to do.
I don't know what to do. I have so much shame, I feel like on a verge of a nervous break down.
Take a few deep breaths and try to calm yourself down. We can always figure out what you should do later, but right now, stay calm. It's important to keep your cool so you can own up to your mistakes and do what is right.