Here is another option I used this past trip which cost me 10k cokones and a quick visit to my Doctor at the pharmacy.
I called AA(favorito airline
) the morning of my departure from SJ and informed the nice lady I was ill after having some pescado the night before, very effective when calling at 5:30 am and having had too much alcohol and sexo 
I told her of my illnes she said if I had a Doctors note they would waive the fee $150 in this case (non refundable seat). Went to tthe pharmacy they filled out an official form put a couple of stamps on it, presented the form at the check in desk and no problemas.
Note, call the AA 800 number as the Sabana office does not open until later in the morning. The 800 number is available 24/7, I would also take the name of the service rep assisting you.
