Yeah, "I just need to say {5 minutes pass}" does indeed sound like a hyperfocus brain dump.
Ideally, that person would get in the habit of redirecting their urgent-feeling thoughts into writing for follow-up at an appropriate time. But they have to be the one to recognize the problem & want to change for that to happen. I was trying to think of a way for you to model / force that pattern.
If you go for a lock, given your health issues, do you think you could get away with a bathroom doorknob privacy lock? So someone can't barge in, but if you have to call 911 no one needs to actually smash the door down?