Ability to sleep is even a little impaired
There was a study done a couple of years ago into what taking a nap for 45 minutes in the middle of the day could do for someone who had a normal sleep rhythm. It found that it could improve your immunity, improve your memory and lower your blood pressure. And it works the same way even if you suffer from shift work syndrome where you have a job where you just can't sleep at night- such as the job of an emergency services worker, a police officer or an airline pilot. If you have a normal ability to sleep, the bottom line is that a little nap midway through your waking hours for the day (or night) will do you world of good.
If your ability to sleep is even a little impaired, if you have insomnia of any kind or intensity, naps can do the exact opposite for you of what you expect them to. Rest yourself in the middle of the day, and you throw your sleep pattern even farther out of whack than it already is. If your sleep problems come through poor sleep habits, jetlag, stress or anything, a mid-day nap can only help intensify the problem. You have a fragmented sleep pattern as it is, and the nap only becomes one more part of it.
Do you find that you're always struggling with having trouble sleeping, fatigued all through the day and that you fall asleep right away that night? That might seem like the very opposite of the insomnia we have been discussing so far; and it is. However, that is a situation that could conceivably signal a problem like sleep apnea - a condition where you just stop breathing while you are sleeping.