On the verge of canceling my trip from NY to Argentina and don't know what to do

I am so ashamed but have been having the worst panic attacks for a few weeks, multiple times a day, about this. I fly often, including internationally, but am so scared about the long leg (about 10 hours) and feeling trapped and having a panic attack. And of course the fears of turbulence and falling which I know are not really realistic. Until this year I've always been able to say I didn't have a visible panic attack or crying on a plane (with one exception as an adult and a few as a baby which don't count). And up til now I've been able to say "I've always gotten on the plane". This fear is so far beyond anything I've experienced before. I am scared to go beyond anything I've felt. And I'm scared to cancel and disappoint my fiancée and of course "what will people think", not to mention losing thousands of dollars. Not sure what I'm looking for by posting here, just hoping someone can help.