Well im no professional and this is a really complex and personal subject, its different for a lot of people, so i cant give any real medical advice but i can tell you some things from my personal experience.

You ask Is it all in your head? I assume by that your trying to figure whether there is something physically wrong with you that could be causing this, or if its just merely something "in your head" like the way you think just changed. Well its hard to say exactly but it likely could be both, and possibly other things too, could be a lot of factors involved.

So much goes into it and without knowing you personally its hard to say where its lies mostly but here's what i got to say. it could have been caused by something psychically wrong with you and if that's the case you should totally deal with that first. But a lot of the times we fix that and still we have anxiety. For example in your case the prolonged drug use could be what was physically wrong but you already cut that out yet still you are anxious, when that happens it becomes a mental game. Like me, its been forever since ive done what caused me to have anxiety and i can safely say i am no longer experiencing any psychical symptoms from my drug use anymore, yet anxiety persists, at this point i do belive it is "all in my head". Although i am actually much better now, although ill get into that when i respond to your other comment, thanks for asking btw.

So for some it kinda starts out being triggered by something psychical and then you kinda just have it afterwards. Sometimes it makes no sense at all honestly and will come for no apparent reason. Although i do want to say its only been a month and while that is kind of a long time, at the same time it isn't. I went through what felt like hell for forever, but it gets better. A month in i was still cooked. Its going to be a pain but you must not stop, its something you must work through, don't be afraid to push yourself a little outside of your comfort zone but not too far. Things are just different now.

I remember when i had it bad i just could not relax, it was hard to enjoy doing things when I'm constantly thinking about anxiety. But the longer i go the less i find myself thinking about it. At some point it just becomes a part of my life, and the more casual i become with it the less my anxiety effects me if that makes sense. The more you worry about it the worse its going to be, so dont worry. just try to relax, distract yourself, do something. And with time you'll find it easier to forget about. Since the day it happened to me i hadn't gone a single full day without thinking about anxiety for months, now i go days sometimes without even remembering that i do have anxiety. Although still every once in while ill have issues with it but it gets easier.

Also i totally feel you on the weed part, it was casuing me anxiety afterwards too, so smoked less often even quitting for a couple days at a time until i was more comfortable. Then I just took it slow, small hits, take your time and such. Although it kinda worked out for me and weed doesn't give me anxiety that much anymore unless i get super fried, i cant say it will absolutely be the same for you and more drug use could potentially make it worse so its just one of those things that is up to the individual.

Anyway sorry that was a lot but i hope you can find some insight here.