Dave usually doesn't like to sleep with his face in a corner. Sometimes he winds up in a funny position, but even then he is usually able to keep a close eye on his surroundings, should anything come up. But here, you can see that Dave has sacrificed this heightened level of awareness for comfort. He does indeed look pretty comfortable. This is a close cousin of Dave's rarely used strategy of napping with his face smushed against the couch, but this version offers even less ability to spot imminent threats.
Fortunately for Dave, threats to his naps are few and far between these days.