I always avoid sleeping during the daytime no matter how tired I am. I have always find that even a ten minute nap seems to deprive me of sleep at night. It may be psychological - but that is the truth. Thus I will read or just have a cup of coffee to avoid going to sleep during the day.
Yes, napping during the day, can keep you up at night; however having a nap during the afternoon can be good for you. Try taking a nap during the early afternoon, keeping to a maximum of 30 minutes long. Any longer than that has a negative effect on your body, and it will keep you up all night.