" To catch up to someone" or " to catch up on something" means that you are behind where you should be and you are trying to get further along to a certain place – here means, just to get more sleep.

“To catch up to someone”或“to catch up on something”的意思是你落后于你应该在的地方，你正试图走得更远到某个地方——这里的意思是，只是为了多睡一会儿。