To tack on to the "Exercise really helps" messages; I can definitely recommend checking your local areas for things like climbing or bouldering gyms (Bouldering is the one where the wall is shorter but more 'technical' and you use crash mats instead of ropes) The people that frequent these gyms are usually real welcoming to new climbers, and the sport itself is a satisfying mix of having a low cost to entry, only being as difficult as you want it to be, thrilling when you finally figure a route or feel yourself progressing, and a little mentally involved (planning routes, judging distances and learning safe techniques)
(There's also a lot to be said for just going for a walk, since that's so cheap it's free, but there isn't aircon :D)
In my mind it's because starting training to take care of your physical health is one of the first steps toward training your brain to take care of yourself as a whole.
It's also a lot easier to feel better about your existence if you have the physical ability to do get up and spend it doing something that gives you joy, like going for a longer walk than usual because the weather hits right
There's also potential link to how we as a species have survived- we had to keep moving to stay alive, so our brains throw a wobbly if we don't.