I wish I had stopped smoking cannabis for good when I had my first break with reality at the age of 19 or 20. I stopped for over 20 years and never had another break. Then I started toking again to treat chronic pain and for energy and sure enough I had a series of breaks with reality for about a decade...
Now I'm done for good. I won't lie and say I don't miss it.
I hope you learn your lesson in a way I never did.
Also there are other antipsychotics besides seroquel so if that is causing side effects you can't tolerate tell your psychiatrist and they can prescribe a different one.
As far as the brain fog you are describing that could be a lingering effect of seroquel or of your episode or both or it could be a new issue unrelated. It could also be a side effect of mirtazapine. The best thing is to discuss this with a pdoc.