IMHO it is very difficult to get an upgrade for medical reasons. Your only chances are either to pay the C fare or to ask friends/relatives who have lots of miles to donate/sell them to you. I have a friend who tried to get an upgrade based on medical reasons, the answer of the airline was that she should not take the flight if she felt that she was not fit for the flight.

My parents did get the exit row on an transatlantic flight based on my elite status. If you know somebody who who has elite status, have them call the airline. In my experience in >95% of cases only pax with elite status get bumped. I always see a lot of people at the gate trying to get bumped, a lot of them have different stories why they should get an upgrade, but it almost never works for non-status pax (in my experience). Personally, I never ask for an upgrade, if I get a bump it's always automatic. I was told at check in several times that I am on the airline's upgrade list based on my status.

Good luck