The fact that you acknowledge that other people don’t deserve to be the focus on your outbursts tells me that you are essentially a decent person. I agree. You do need to figure it out. You could hurt somebody and you could end up in jail.
If you could get to the bottom of this yourself, you would have done it already. The way to get some answers is to see a mental health professional for an evaluation. In addition to the episodes of rage, you also seem to have self-esteem issues. Working together, it’s likely you and a therapist can discover what is going on. Your therapist will then make suggestions about what you can do about it. It’s a team effort that will only work if you are an active member of the team.
You wrote an honest, intelligent letter. That was a good start. Now make an appointment. Take your letter with you to jumpstart your session. There is no reason to go through life feeling as you do.
I wish you well.