There's a wide variety of ways HDR brachy is done, so it will help to say which hospital to get direct experiences of their procedure.
Some keep you under general anesthetic for the whole procedure, but that can be hours and rules out some patients from being able to have it. Others just use a spinal block or short anesthetic for the brachy catheter insertions, as the rest of the procedure isn't painful (and this works well if they're doing several patients together on a production line).
Some do two fractions (sessions) on one hospital visit a day apart, others do them 2 weeks apart (or a week apart in your case).
I had just one session, the other being replaced with external beam (which is called HDR Boost).
When I went home, my bladder capacity seemed to be tiny and I had urgency to go. However, each day saw a doubling of bladder capacity and it quite quickly returned to normal. I also found I had started peeing about 10 seconds before I expected to, which was on the way to the bathroom. Having worked this out, I started engaging pelvic floor on the way to the bathroom to prevent leaking. I had a very slow continuous leak of both urine and blood which didn't seem to relate to urgency, but this gradually reduced to nothing over the next 4-6 weeks. I wore disposable pants for a couple of weeks, and then a female sanitary pad for about a month.
It made erections shorter and painful, but that slowly recovered over the following 3 months back to normal.
I would suggest you get doing pelvic floor exercises now. If I hadn't done them, I would have struggled to remain continent in the couple of weeks afterwards.