I believe a big factor is what your eating as a less toxic diet. That is to say, some diets are better are easing detox symptoms and some diets (imo) recirculate a lot of the dislodged toxins in your body and cause much longer lasting and stronger symptoms. Of course the relative health and toxicity of your body when you start is also an issue.
I believe that raw fats (animal in particular) are the best nutrient to ease detox symptoms and help usher toxins out of the body. So someone going on a lower fat diet might experience more detox symptoms for that reason.
When I first went raw vegan I was praying for something profound to happen, even if it was miserable, to validate that what I was doing was working and giving me results. I was also consuming very low calories when I started, and will probably never know which experiences were detoxification, which were caused by lack of certain nutrients, and which were relatively unrelated to diet.
One thing is certain though, everyone is always detoxing, even SAD eaters. If toxins weren't constantly leaving your body you would be in serious trouble. A lot of mystery and hype is given to "detox" when in reality it's just a simple law of nature, a combination of diffusion and organ activity. Everything in nature moves from areas of greater to lesser concentration (unless counteracted by an organism or outside force) and toxins in the body are no different. And of course certain organs, in particular the liver, are given the specific job of filtering out toxins and having them removed. Some of the raw vegan books I read before seem to suggest that you will go through terrible pain and discomfort and emerge a super version of yourself. This is a great selling point but in my experience (and of those I've read about and talked to) falls short of the reality.