I think I'm losing it...?

I'm not sure if I'm having severe anxiety or if somethings actually wrong with me?!? I smoked from 16 to 26 and a few months ago started worrying about lung cancer/ COPD so I quit smoking. I was worried something might be wrong with my heart also at the time, so I went to doc who gave me EKG and blood test, said I was having panic attacks and perscribed me wellbutrin. Recently I'm also worried there is something wrong with my house (I know I'm sounding crazy now) so I bought a carbon monoxide detector, and a radon test, etc... I think I'm cancer riddled or something, it's like I just realized my own mortality. Lately I've felt like my throat is closing, I'm not sure if its allergies, COPD, something with the HVAC in my house, or if I'm actually just going crazy. Not sure what to do anymore.