I was working on a dance and i got a pain in my upper chest. it went away, but now i feel very tired and weak. i'm eighteen. should i be concerned?

No! At your age ---: Definitely no. I would rest for a week and do stretching exercises and restart the dancing routine again. If the symptoms return, or if you are still concerned, see your pcp then.

No. But you should: See a heart doctor. While it is rare, hypertrophic cardiomyopathy is an issue that should be ruled out. While some will tell you should not worry, I am telling you worrying is of no benefit. Getting evaluated by a heart doctor is of benefit. Then after that you could exercise without worrying! http://www.Mayoclinic.Com/health/hypertrophic-cardiomyopathy/ds00948/dsection=symptoms.