My recommendation would be to coil it into a carpet, it's be the easiest and most comfortable, but it wouldn't stay together very well. You could put your tarp over top if you have a rope tarp, that would help keep it nicely coiled a bit, but tossing and turning at night would eventually end you up in the same position as just messily flaking your rope out.
Start in the centre and coil the rope round and round until you have a mat like so:
Make two round coils, or fold your rope at about 5ft long then coil along the length so you have a longer mat to sleep on.
Another option, which will take a lot of time to tie and untie, and no small amount of skill, is to weave a mat:
This option would take hours, but if you're stuck with nothing to do, it could help you pass the time.
Personally, I wouldn't want to sleep on my rope for fear of doing some unseen damage to it, even though it's unlikely you'd do any damage to it on a clean floor.
Maybe include in your rope log that the rope was used to catch some Zzz's.