Breathing meditation can be very useful when you start feeling anxious - it engages your parasympathetic nervous system and calms you down.

Basically:

Sit (either in a meditative position or on a chair, try to keep your back straight) with your eyes partially closed (I usually do with eyes fully closed when I meditate), and breathe in slowly (maybe to a slow count of 4) - hold your breath for a moment - and slowly release your breath at the same speed. Breathing through the nose is preferable.

Your mind will be pretty busy - but that's ok, the idea is to become aware of your thoughts and to calm the mind so you can be calm, and present. The key is to focus on the breath itself, that is the object of your attention. If meditation isn't something you're used to - you're likely to find your mind begin to follow random thoughts that pop in your head - when this happens simply tell yourself "return to the breath", and then do so. Don't fight the thoughts, just let them float through your mind and dissipate, without following them or feeding into them (when you fight or follow them, typically they're given strength and stick more in your mind).

If you have a smartphone, there's meditation timer apps, if not, there's onlinemeditationtimer.com (you don't want something that's grating and jolts you like an annoying alarm clock). 5 minutes is a good start (twice a day if possible)… if you're not near any timer, just do it for what seems like a little bit and until you calm down. You might not be totally calm, but it can make a world of difference - trust me. It might not take the anxiety away totally - but it should help quite a bit with dealing with the anxiety, and even may help with other symptoms you listed, from not having cannabis.