Oh boy! I know exactly what you're saying!
My last attack, like yours, happened about 2 weeks ago... in the shower, no less.
You start thinking of one negative thing that happened, maybe yesterday... a month ago... 20 years ago... that leads to another... then another... and before you know it your head is spinning. Then the tears start, you feel like you are coming apart. "When does it stop!" you're mind is screaming!
I've been there sooo many times over the years, it's not funny.
The one thing that has stayed with me from my therapist, is talk therapy. Let me see if I can explain it right.
Using my episode as example... I had to mentally tell myself to knock it off! Let it go! Then quickly switch to thinking about what's good in my life. Watch only happy things, if you are a tv buff, comedies, Golden Girls is always good... stay away from anything negative as much as you can. When you start with those thoughts, don't let them continue... stop them in thier tracks. Try to journal... maybe writing these thoughts down when you have them, will help you to release the pressure some.
Come here and vent... go outside and just have a good scream.
You are not a lone.