I Find It Difficult to Breathe with Invisalign and May Be Allergic

You should talk to your Invisalign provider to see about a refund.  The fee he or she  paid to Align (the company that makes Invisalign) is not refundable but depending on how much you paid you may get some refund.  You might also consider sensitivity testing to see if you really are allergic to the plastic in the aligners, although this too would cost something.

It is possible to be allergic to just about anything!  Having said that...reports of allergies to Invisalign are extremely rare.  Certainly you should talk to your doctor about your symtoms and see what he/she says. 

I would think that if you are unable to continue treatment, the doctor would refund you your cost minus the work that was already done and the Invisalign lab cost, at least that is what I would do!