Why and how were the three friends feeling sleepy?

From the text:

Harris said he didn’t think George ought to do anything that would have a tendency to make him sleepier than he always was, as it might be dangerous. He said he didn’t very well understand how George was going to sleep any more than he did now, seeing that there were only twenty-four hours in each day, summer and winter alike; but thought that if he did sleep any more, he might just as well be dead, and so save his board and lodging.