Had a less horrible night, still woken by painful erections but managed to at least get a few solid hours of sleep.
The catheter night bag was really full and difficult to empty. When I cut the corner off a jet of urine sprayed the area around the toilet, so I had to wipe it up and mop the bathroom.
I managed to poop for the first time in four days and without any spasms. I’d avoided caffeine during the day, so maybe that helped.