My longest stretch reading a huge novel from cover to cover was around 11.5 hours, that included placing it IN the fridge so I could continue reading while getting some food, without really breaking off the contiuum.

That might have broken something minor in my brain haha, was not able to do more than 4-5 hours from then on...

Now? Who knows, but recently when I had a 4 day and night stretch of not being able to sleep for more than 5-10 minutes before getting strangled I did read one very verboten book in one go, so its still intact :-)