Something I've realized over the years, through periods of smoking/not smoking, though phases of acute anxiety and paranoia, and phases of literally no anxiety for months....
BREATHING!!! it's the answer!
The feeling of anxiety is mostly caused by not breathing in enough oxygen. Your brain gets deprived, and you start to feel dizzy, your hands/feet/face may start tingling, and you may black out or your vision gets messed up. It's from
hyperventilation or the opposite, holding your breath without realizing you're doing it.
I've gone through so many marijuana-induced panic attacks and regular panic attacks to realize, that a very very quick and reliable method to controlling these when they happen, is to simply BREATHE. Slow. In through the nose, deep into the chest and diaphragm and stomach, and slowly back out through the nose. Breathing through the nose is very important. Breathing too quick and shallow will cause hyperventilation. Anxiety often causes you to unconciously "squeeze" or tense up your body and hold your breath. Do you often let out a huge "sigh" for no reason? This is why! Whenever you find yourself having an intense moment of anxiety or panic, especially while smoking, which decreases the level of oxygen flowing to your brain, just take a step back, concentrate on your breathing, and it will go away.
Getting up and walking or stretching out your chest/shoulder area also really helps get the oxygen flowing back into your system, and relieves so much tension!
If all else fails, make some green tea or mint tea, which is calming and will help relieve anxiety.
Hope this helps someone else out there, because god damn I know how shitty and terrifying it can be, and it does not have to be! :D
Peace... xo