I don't think OP indicated the nature of the medical condition, I assumed he has had medical clearance and assumed it was not cardiac related.
I have always had some timing issues with the ticker giving me sleep issues. I had some issues leading into PBP and ended up seeing 4 different Cardiologists (One surgeon, one EP, Two sports specialist Cardiologists) with all the tests, some twice. They all said I should do my long distance riding and were 100% supportive. If OP has not been cleared and checked for whatever ails, he/she should do so for sure.
To get a true 8 hours straight sleep on a grand randonnee, it has to be a hotel room and that is the logistical challenge in rural france. My plan in 2019 was to sleep a long sleep in Brest and I had a hotel booked, I just made the stupid mistake of thinking it was going to be easy to find. I ultimately gave up looking for it and slept at the control Monday night. If a rider can get to Brest Monday night (say 28-30 hours), they have essentially two full days to return back making it a hard 600K and a leisurely touring 600k. There are quite a lot of hotels about halfway back in Fougeres, too.