The problem is not that I took a nap, but that I wore myself out. I have fibromyalgia, and my life is a balancing act between doing too much and too little.
Today I'll just walk; tomorrow I'm going to sculpting class again. I really liked it. I haven't tried the Pilates class but when I did it at home it hurt my back a lot.
I've learned to listen to my body though, so hopefully it won't hurt next time, and I'm also more flexible thanks to the weekly yoga class.