I arrived in LOS on 12/25 and was planning to leave on 1/25 but now I will have surgery on 1/25 and staying at least 5 days past the 30 days for recuperation. I have two questions:

1) I am in BKK, is it best to go now to immigration and see if I can get an extension for 5 days. And if so, where is the office.

2) Or is it better to just show up at the airport and pay the fine at that time. And if I do this is there any chance they will waive the 500Baht/day fine because of the surgery?

If having real medical treatment hospital can help you obtain extension of stay. Or you could just show your ticket out and obtain 7 days for payment of 1,900 baht at immigration before treatment. The office is end of Soi 7, Chiang Watanna Road.

As said, contact the hospital. Many of the private hospitals have liasons with immirgation and will be able to help you get an exension of stay.

The office is end of Soi 7, Chiang Watanna Road.

Is this BKK?

Yes. Look Here.