Lymph fluid, which we have 6x the amount of in proportion to blood, is loaded with toxins on a traditional diet. Muscles, skin and bones can also store toxins when the body runs out of fat to put toxins in. The brain will even begin to store toxins when everywhere else is full. When your body finally stops being flooded by constant toxin intake (such as cooked proteins, cooked fats, refined sugars, refined flours/rice, artificial sweeteners, artificial colorings, etc), then the blood becomes clear enough to handle a load of toxins to be expelled from the body.

The state of your blood determines how you feel at any given moment. It's bringing the oxygen and nutrients to your muscles, brain and organs. When detoxifying rapidly, the blood is full of toxic matter which can cause muscle cramps, clouded thoughts, lethargy, frequent bathroom use (although most people use the bathroom about one in four times to what a healthy person should), etc. This is why every decent book about "going raw" mentions the "transition phase" where all processed foods are avoided, but baked yams, steamed vegetables, and brown whole long-grain rice are part of the diet. These cooked foods thicken the blood in comparison to raw foods, slowing the detoxification process.