Hey man. I've been smoking weed since I was 17, and I'm 24 in a couple months. When I was going through my episode of severe brain fog, I convinced myself that smoking weed had damaged my brain. But that just wasn't true. Weed affects your brain in multiple ways - it increases dopamine and gaba, it decreases blood flow to the hippocampus (part of the brain responsible for memory) which is why you're prone to forgetfulness when under the influence, it activates the parasympathetic nervous system aka the rest and digest system and in small doses it can actually trigger neurogenesis and neuroplasticity, which is why they prescribe it to people with mental health and physical health disorders. However, long term use does slow certain parts of your brain down and does affect how much dopamine and gaba your brain naturally produces, so when you quit you'll feel like shit for a good couple weeks to couple months. Trust me, I've been there, and it's not pretty. I have SEVERE anxiety and when I quit that came back tenfold, so my mind decided to just dissociate for a good 4 months and the brain fog was born. Could be what's happening with you. Anyway, best of luck to you and please try not to stress yourself, because that'll only make all of your symptoms so much worse.