All's good :D

It's probably better to run a level over it (so the the level is ... level) and to express things in feet & inches (or meters & mm). So you end up with something like ... "my bathroom's 8'6" across, and has a fall of 2¾" ... " - because anyone that would work on your floor is going to want hard numbers, and someone's going to have to translate those degrees into inches anyway. Get rid of the unnecessary complication - it's like giving your address as a GPS coordinate and height above mean sea level instead of saying "1234 Main St, Pleasantville".

A 13° slope is practically unusable. That amounts to a drop of 2¾" per foot, or a full step every 2.5 or 3 feet. On a small bathroom (since we don't have the dimensions) that could mean a drop of 1.5 to 2 feet.

You'll be replacing the whole floor, and much of the subfloor and piles, so you may as well decommission the bathroom and rip the flooring out. That'll be much easier than going into an underfloor crawl space and finding the sinkhole to hell is full of the contents of a broken sewer pipe.

Are you positive it's 13°? ... 1.3° would already be bad enough, but 13° is beginning to sound like someone just laid flooring on top of a [shallow] staircase.

We didn't quite get to prohibition in New Zealand, but we (along with Australia) got what became known as the "six o'clock swill", because it was a race to get as much beer in from the end of the working day until the pubs shut an hour later.

To get around this one notorious pub started serving 'meals' that were nothing more than a bowl of rice. For 2/6 (approx 25 cents) you'd get an extra four hours drinking time.