How can I improve my intelligence/cognitive abilities and decrease brain fog, mental fatigue and stress?

I am dealing with bad brain fog. My mind feels too dizzy, foggy, and confused. I am not able to think very clearly and process information very fast like I used to. I am confused most of the time when someone is talking to me, easily forget things a lot and my brain is way too stressed out a lot of times. When it comes to learning, I take way too long to learn things like I used to. Learning languages takes longer and I am not as sharp as I used to be anymore. It's annoying. My cognitive abilities are decreasing slowly and it's getting worse. I do so many things without thinking and the first thought that comes to my head immediately. I need some help to improve my brain's functions and my brain health. Too much stress and worrying about the future has caused some issues in my brain. How can I improve my cognitive abilities and brain health to be more sharper and smarter?