How to ‘switch off’? My brain never stops and I’m exhausted

I try to distract myself. In no particular order:

• Play my favourite music and try to really "get into it". A dark room helps. I might throw in some stimming.
• Go for long walks (10–12 km) at a slow pace. Podcasts and music pass the time. I pay attention to all the little natural details around me.
• Read a book. I pick something interesting or entertaining—anything to hold my attention—it doesn't have to be "worthy". I often pace about when reading. I read for two to four hours per day.
• Watch some sports on TV. Climbing, cricket, motor racing, football, cycling, athletics, ... whatever holds my attention, even briefly.
• Watch my favourite TV shows. Usually comedies that will cheer me up. Documentaries can grab my attention.
• Fake a smile. I just make a big grinning shape with my mouth when I'm on my own. Seriously. It's backed by science.
• Talk to a GP or therapist. See if there is anything they can do to tide you over.
• Get things down on paper (or forum) and out of my head.
• Learn about how my brain works and come up with cunning plans to outflank it. I "step back" and observe what's going on. Most of my intrusive thoughts are lies. I call them out.
• Recite a mantra. "This will pass. I'll be OK. It's not my fault. It's just my brain."
• Talk to my wife.
• Wait it out. Recovery takes time. Expect gradual improvement with dips along the way.

I try to distract myself. In no particular order:

• Play my favourite music and try to really "get into it". A dark room helps. I might throw in some stimming.
• Go for long walks (10–12 km) at a slow pace. Podcasts and music pass the time. I pay attention to all the little natural details around me.
• Read a book. I pick something interesting or entertaining—anything to hold my attention—it doesn't have to be "worthy". I often pace about when reading. I read for two to four hours per day.
• Watch some sports on TV. Climbing, cricket, motor racing, football, cycling, athletics, ... whatever holds my attention, even briefly.
• Watch my favourite TV shows. Usually comedies that will cheer me up. Documentaries can grab my attention.
• Fake a smile. I just make a big grinning shape with my mouth when I'm on my own. Seriously. It's backed by science.
• Talk to a GP or therapist. See if there is anything they can do to tide you over.
• Get things down on paper (or forum) and out of my head.
• Learn about how my brain works and come up with cunning plans to outflank it. I "step back" and observe what's going on. Most of my intrusive thoughts are lies. I call them out.
• Recite a mantra. "This will pass. I'll be OK. It's not my fault. It's just my brain."
• Talk to my wife.
• Wait it out. Recovery takes time. Expect gradual improvement with dips along the way.

I like to read up about the music as I listen to it and get flappy hands when I resonate with the information and the music i dotn know why but flappy hands make me so happy it’s like they release dopamine levels nothing else can 

Damojo said:

Fake a smile. I just make a big grinning shape with my mouth when I'm on my own. Seriously. It's backed by science.

This is true - I do this too and it does work.

As an aside, I had a neighbour who tried something similar but with laughing. He tried to start out with loud, extrovert laughs to cheer himself up and it seemed to work for a while, but after a few weeks (we could hear him through the thin walls of the flat) the laughing would slowly shift into crying then almost wailing.

It was quite heartbreaking to hear and while we did ask him if he was OK (without mentioning it explicity to avoid embarrassment) he didn't want to engage in conversation.

He eventually moved out which was a bit of a relief but left me wondering if there was more I could have done.

Sorry, that was a bit of a negative aside, but back to the point - smiling sincerely does help a lot:

https://www.verywellmind.com/top-reasons-to-smile-every-day-2223755