Extreme Pain: HELP

I have good news and bad news. The good news: This December I'll be visiting my dad, who's stationed in South Korea on an Army base, as a combined Christmas/Graduation gift. The bad news: eve has told me that I'll be on my period the entire time I'm in South Korea. I have extreme, EXTREME pain during my periods (so extreme that my doctor is convinced that I have endometriosis. I just haven't gotten a laparoscopy yet). I don't know how I'm going to manage a 20+ hour flight while trying not to vomit/scream/writhe around/cry/pass out from the pain. What can I do to survive this trip and eliminate as much pain as possible? Please help, I'm panicking. I really really want to see my dad, I haven't seen him in so long.