|Sometimes a poorly timed nap can turn you into an insomnia vampire...|
Your body has two cycles during the 24-hour period we call a day: Wake and Sleep. Generally speaking (and science confirms this), most human beings function best when they are awake during the day and get their sleep at night. This is due, in part, to the way we relate to circadian rhythms. We tend to rise because our body is stimulated by morning light and that turns our pineal gland's production of melatonin down so we can wake up and go about the day doing the things humans do.
There's another process in play, however, that most people aren't aware of. Just like with hunger, thirst and sex, our brains have a built-in sleep drive. How it works is pretty simple: our drive depends on how sleepy we are. If you sleep a solid 8 hours on Monday night and then go to bed at the same time on Tuesday night, you will be sleepy to more or less the same extent. However, if you have really fragmented sleep on Monday night and then go to bed at the same time on Tuesday night, you will probably be more sleepy than you were on Monday night because your body did not get enough sleep to fulfill all the physiological demands that the process of sleep takes care of. With any luck, Monday night's crummy night of sleep will be replaced by a solid night of hard sleep on Tuesday.
Unless you decide to take a nap late in the day...
How do naps enter into this equation?
Naps are a good thing for people who are young or old, as their bodies require a little extra sleep to keep up with various physiological processes at play. Also, people who work night or overnight shifts can benefit from naps prior to their shifts because they can, in essence, make a deposit in their own personal sleep bank account so as not to accrue any sleep debt while at work.
However, if you are a normal, healthy adult with lifestyle that suits daytime work and nighttime rest, you are cautioned against sleeping in the late afternoon because, in doing so, you might rob yourself of some of the sleep drive that will help you get a full night's rest that night. Taking a short nap after 4pm can mean that at 1am the following morning, you might be finding yourself staring at the ghoulish circles growing under your eyes as you struggle to fall back to sleep. This can lead to more daytime sleepiness and potentially more naps at later times in the day on the days that follow, all of which messes with both your circadian rhythms AND your sleep drive.
So if you had a bad night of sleep the night before, put off the nap if you are able to, and just go to bed early the following night. This is the easiest way to put you back on trap and keep your sleep drive from falling out of rhythm.