For those wondering how to nap at the office and not get hauled into the managers office for sleeping on the job, I paraphrase a tip from Scott Adams (Dilbert):

"Grab a handful of paperclips and find an office/meeting room. Shut the door and lie down on the ground with your feet against the door. Sprinkle the paperclips in front of you. Now have a nap.

If someone tries to enter the room, the door will hit your feet. This will naturally cause them to pause (and stops them entering), it wakes you up and lets you reach for the paperclips which gives you a ready excuse ("Oh sorry, I was just picking up the paperclips")"

:)