I did a brief for uni last year which involved me looking at afternoon naps - and their place in the work place, in depth.
Based on Nasa research, if you nap for between 15-25 mins (no more) between 12-2 pm it is better for your mind than an extra hour in bed in the morning. Also work productivity is raised 80%!!!!! If you nap for longer, or out of these times, it has the oposite effect. This is Nasa based on nasa research.
Also, in places where a siesta is commonplace, heart disease is much lower too - great for blokes. It also helps your metabolism too, not to mention general stress and living longer.
Google actually have sleep pods in their office for drowsy staff in a post lunch slump. They're doing alright for themselves aren't they?
xxx
For those who're not allowed to snooze at work (ie everyone) avoid carbs on your lunch - they kicks ur ass. xxx