What if something else happens during that time?

1k$ surplus income per month on a 18k$ bill means you'd have to forfeit all surplus income for 18 months.

If any other medical emergency happens and you have another 18k bill? Or a car accident (of which there are a lot)? Or car just breaks down? What if you get fired and spend a few months searching a new job?

This isn't exactly financial security with such a bill pending over your head plus numerous other bills being a possibility.