I know what you mean about the anxiety. I went through an episode during my teens (many years ago) ago where I was suddenly finding myself ridden with anxiety in totally normal situations after getting high. My relationship with the beloved bud had gone askew, it seemed. Every time I smoked I would just feel all paranoid and racy and I didn't like it. But why? I didn't know. This led to one of the greatest shifts in my life, as it led me to quit marijuana fully for a year.
I knew that I didn't want to smoke weed anymore, but I also knew I would if I just kept doing the same, and hanging with the same crowd. I had to keep myself occupied, and so I got into martial arts. Next thing I know, I found myself at the gym 5 times a week. About 9 months after quitting weed cold turkey I competed in my first amateur kickboxing match, and I won

The night I won my first fight, I got blasted. I drank and smoked weed all night for the first time in ages. What I realized was, I already knew before I smoked weed that I wouldn't feel anxious. How on earth could I feel anxious? I just won my first fight! Life was good! How could there possibly be any anxiety present after dedicating myself, aspiring and achieving in such a clear and present way?
I think that anxiety is an almost subconscious indicator that the direction we are headed doesn't jive with what we really want out of life. Whether we are conscious of it or not, this "disharmony" manifests itself as anxiety, and anxiety's job is to wake us up, let us know that something is wrong and needs fixing.
For me, in hindsight it seemed like I never would have gotten into martial arts without that bout of anxiety. For my whole life, ever since I was little, I had always wanted to get seriously into martial arts, and the anxiety hit me right around the age that became possible. I was in the stoner crowd at school, so without the anxiety, I could have easily just kept smoking the days away, finished high school, and never taken that year off marijuana to turn myself into a beast. Perhaps my subconsccius mind had realized this, making me anxious towards the repeated behavior which would lead to an undesirable future. It's the only explanation I've come up with that makes sense to me as per what I experienced.
The values instilled in me through martial arts allowed me to find a sense of balance between work and play in my life, and eventually made me into the person I wanted to be. These days, I enjoy martial arts AND weed.. sometimes, at the same time

It's been 10+ years, I've been yinning, yanging, and puffing anxiety free ever since, but I never would have got there mentally without quitting for a year, and I have anxiety to thank for that.
Perhaps on some level, you are realizing that the daily marijuana use is no longer serving you in the way it once did, and is now perhaps even limiting you? What is it you are "moving towards" these days? Would marijuana every day help or hurt that objective? Whatever the case... something's amiss. That's usually what anxiety means. If smoking weed is making you anxious, is there not something else you should/could be doing which weed doesn't allow you to? The answers may not be as clear as you think.. perhaps not even conscious.. you may have to dig. Just try to be honest and open with yourself, and search your feelings when there's no words.
My advice would be get busy. Get active. Do stuff. Doesn't have to be martial arts, but find your own version of something you can be passionate about, and progress into it. Sitting around thinking about how much you miss the beloved leaf and wondering about this anxiety isn't going to break you through to where you need to be, and could also be contributing to your percieved cognitive decline. IMO, since anxiety is a call to action of sorts, the only cure for it is to take action. It's not something you can "think away". I imagine it would do wonders for you to get excited about something else for a while.
Lastly, being Nexians, we sometimes put extra emphasis on the cognitive aspects of being, but don't forget about the fact that although temporary, part of YOU is a body made out of molecules and is subject to all types of physical-ness. The lothargy and mind going blank stuff could easily be related to diet and exercise. It sounds like something I've had experience with. Look up "hypoglycemia" and see if that rings a bell.. it's a glycemic condition producing symptoms much like you described, which can be completely controlled and rectified by putting the right stuff in your body. Don't be afraid to see a doctor (or two) about that stuff either.
In reading your post, I wasn't sure how to respond myself, but I knew I should... so I just started typing. It seems to have come into focus now.. hope you can glean a thing or two from my little story. Good luck in there

*** causmic is a figment of your imagination. A manifestation of your own consciousness and a projection of mine. causmic is a fictitious and wholly imagined character, and through his/her/their imagined life I share metaphoric, poetic, and abstract streams of consciousness, and although may provide statistical or scientific fact, any and all information posted by causmic is in the form of an imagined and entirely theatrical persona, tall tale, or cleverly faked photograph(s). Nothing I/we say has any basis in reality. All descriptions of events are fictitious, for entertainment and educational purposes only, and any similarities to real persons or situations existing on planet earth are entirely unintentional and coincidental. Nothing posted is to be taken "as fact". The information provided by "causmic" is assimilated at your own risk. By reading the posts made by "causmic" at "dmt-nexus" you have agreed to these terms and waived the account holder(s) (causmic) from any and all liabilities and/or consequences relating to and/or stemming from the (fictitious) information contained therein. ***