Cats can spend 18 hours a day sleeping. As they are solitary animals, they want a safe hiding place to snooze.
But a cat curied in a tiny box, even out in the open, is probably just avoiding your cold floor. Cats are happy in room temperatures around 14 degree Celsius warmer than in comfortable for human, and if there isn't a convenient sunbeam to lie in, they will make do with a cosy shoebox.
Sunlife, March 25 2018