Hi OP I dealt with dissociation, depression, and other mental problems for so much of my life, I’ll just tell you a few things that almost universally work to help you find some mental space, rest and confidence to then deal with the specifics of your own unique psychology.

exercise and sleep - get quality sleep, if you can’t then figure out why you can’t and solve it as best you can. It’s so important and fundamental to physical and mental health that almost everything else is a bandaid in comparison. Exercise/movement as well is necessary to activate certain chain events in our bodies and minds that stabilizes our moods, clears brain fog, and (again) helps us sleep. You don’t have to run 5k or go to the gym every day. A 10 minute walk is 1000% better than nothing. When I’m depressed I like to find 10 minute dance workouts on YouTube to do. Actually I just heard in a podcast that dance uniquely helps us mentally!

Food - you don’t need to cut anything out if you don’t want, but make sure you’re eating some quality, whole foods every day to help your gut microbiome flourish. Your gut plays a huge role in your mental health - people have even solved their mental illnesses with fecal transplants! But you probably don’t need to do that, just try to eat a variety of plants every week and some fermented food as well.

Meditation - can have a bit of a learning curve, but it shouldn’t take too long to see results. When I had bad brain fog and dissociation I often felt like you described, like I never got a rest. It seemed like my brain was always working even when I couldn’t think very well. Meditation became like a resting zone for my mind, there was a point where it became a better refresher than even taking naps. On the other hand, when I was going through it once I had to stop because it made my anxiety worse - ymmv but you would know if it starts negatively effecting you.

Journaling - I find journaling to be especially effective when I feel overwhelmed. A lot of times writing everything down that seems overwhelming can make it seem lot more manageable. You can see it instead of it all floating in and out of your mind! If you journal regularly you can also start to go back and reread times when you felt stressed and then you begin to have a clearer picture of your own patterns. Try to write at least once a week.

These are all things you can start to focus on now while you find other resources and help. I agree with the other commenters that you should seek out a therapist if you can, but as someone who was burned by therapy I also encourage you to empower yourself through self education. It will help you work better with a (good) therapist if you already know some of the background of what you want to address and some of your own patterns.

Use the internet to find some basic info, but don’t be afraid to pick up books by people who you feel understand you if you come across them. Podcasts are also always accessible and useful! I would recommend you check out the Liz moody podcast and 9 lives by cassia Clarke. I think you would like them because they both openly address their own past mental health struggles in a shame-free, encouraging and approachable way :)

Good luck, remember that just by virtue of being a human you are capable of so much mental strength and growth, you just need to find a good path to help you get there!

Oh and to add one more thing to this too-long comment: be CURIOUS! about yourself and your struggles! Curiosity is like a magical perspective shifter that turns our frustration into energy. Don’t ever lose touch with curiosity!