Anything above 12 hours is painful.
Anything above 15 is every fiber of your being physically screaming out "WHAT ARE YOU DOING, YOU LUNATIC? WE'RE ALL GOING TO DIE!
And you see with clarity unlike any you've ever experienced that reality is actually just a flat projection on some thin membrane ahead you, kept just out of your reach.
It's a fairly convincing illusion, until the worms that live behind it wander too close to the surface.