How much do you sleep per night and how much caffeine do you drink?
I used to nap like that too, until I reduced my caffeine (one cup of coffee in the morning now) and started consistently getting 8-10 hours of sleep per night. I'm much happier and more productive than I ever was when I felt like I was constantly battling exhaustion with afternoon naps and coffees.
Now that I am self employed as well, I try to, but it just makes me want to sleep the whole afternoon. It's either sleep deprivation, or Italian genes :)