Ever wonder why you have to fight the urge to sleep after lunch (unless you're lucky enough to work from home and can give into it)? Your body's circadian rhythm is in a natural resting place after your noontime meal. There's also another system called the sleep/wake homeostatis that tells your body when it's time to sleep, which also occurs after you've been awake for a long time. By 2 p.m., you've usually been awake for at least eight hours. Put those two systems together, alongside a heavy lunch, and it's no wonder you want to take a nap [sources: National Sleep Foundation, Korkki].
Not everyone has this feeling to the same degree but it is a natural one. In fact, for most adults, their strongest sleep drives are at 2 p.m. and 2 a.m., thanks to their circadian rhythms. However, if you got a good night's sleep, your urge to nap at lunchtime will be lessened [sources: National Sleep Foundation, Korkki].