WebMD Health News reports a small British study that suggests that a short siesta or a jolt of java help combat the mid-afternoon nods.
What doesn’t seem to work, the study showed, is trying to grab some extra winks in the morning in an effort to ward off problems later in the day.
And, of the three, the nap is best.
My Take?
My good friend, Obstetrician-gynecologist, Fred Brown, M.D., takes a short afternoon nap each day. He believes it makes his entire day go better.
And, many of my patients believe, and a number of other studies have shown, that a short midday or afternoon nap also increases job performance. 
It appears that a 15 – 20 minute nap has the best results.
I also advise my patients to avoid drinking or eating caffeinated foods or beverages (coffee, tea, soda, chocolate) after 4 p.m., as it can last in your system for 6-8 hours.