Megan-

Smoking can cause increased heart rate, blood pressure, etc. There's a possibility that what you smoked could have a higher concentration of THC- THC is one of many cannabinoids (chemicals in cannabis which cause psychotropic and/or gastrointestinal effects) in cannabis; a higher concentration of THC itself is linked to anxiety and paranoia, while other cannabinoids are linked to relaxation, etc.

This ratio is shown through the differences in sativa and indica bud- sativa has a higher rate of THC than other cannabinoids, thus giving more of a head high (smokers who are prone to anxiety have an increased risk of feeling anxious, paranoia, or panic) whereas indica has less THC and more of the relaxing cannabinoids.

Because I assume you're under 30 years old (please tell me if I'm wrong!) you're at an extremely minute risk of a heart attack, unless you have congenital heart problems to begin with. The pain in your chest could be caused my a constriction of tiny blood vessels- capillaries- called angina, which produced that left-arm numbness and the tight-chested feeling. More likely than not- having experienced panic attacks myself- it was a panic attack made worse by smoking.

Don't smoke until you feel you're calmer. Take deeeeeep, slow breaths- try meditation for anxiety and panic attacks. I had severe anxiety problems when I was younger, and meditation has transformed me into a much calmer person. Also, are you seeing a therapist for your anxiety issues? Therapy is a WONDERFUL tool to learn how to deal with anxiety, it's helped me immensely. If you need any resources or help, let me know.

Take a break from smoking, and then slowly introduce it back into your life. If you're fortunate enough to live in a place with an abundant weed variety (i.e. CALIFORNIA) then try to see if you can get a supply of indica buds. More likely than not, you're stuck with whatever your dealer has, so in that case, take it slow.

Best of luck! Anxiety and panic attacks are devastating, but you can improve your condition!