I used to take Sunday as a rest day when I first started exercising and it wore me out to do exercise levels that I now hardly notice. So, I work out 7 days a week now, only skipping it if I have a conflict (and usually I will find a way to get some work in somehow). I find that if I don't exercise, I just don't feel right the whole day. I will cut down if I'm feeling very achy or tired, and I have a routine set up so that I don't fall into that situation too often anymore. Just really like to exercise and it only seems to be doing good things for me, so I just keep up with it!