I agree with all of the great suggestions you have been given. As for me personally, I could never " willfully control " all those unhelpful thoughts that flood my brain. What had happened was my brain developed these continual " loops " of negative thoughts that I could not break. I believe it's a law of physics that two " things " , physical or mental, cannot occupy the same space at the same time.
If you can just focus on the " now" , what's right in front of you , not the past or the future, you can " shut out " those thoughts that hijack your thinking.
Look at it like a greeting message on your answering machine that you decide
to erase and put in a NEW one ! In your brain it's called neuropathways.
You can develop new ones.
It may sound complicated but it's really not. Just takes practice.
And I have to start using the other half of my brain which is not emotional,
but practical and realistic. A part that got little use over the years.
The bottom line is that we can get through those times where we feel
there's no way out. We just have to be fortunate enough to learn how.
Mindfulness, that's what it's called.
Best to all...