It's my personal opinion that most who go on a detox for the first time have many problems due to the shock to their system. Your body isn't used to these "foreign" bodies we introduce through our diet (and other ways), but it does the best it can to deal with it. To then start a detox would put your body into warp speed trying to get rid of years worth of what it deems as not needed. That's enough to make you feel bad because your body is in overload. That's a lot to ask of your body. Expect to feel bad. I would personally equate it to starting a workout regimen and your body hurts like heck for the first week or so until your body is used to the extra stress. Then, it's smooth sailing for the most part.
I know the first couple times I did it, I felt really bad. Now, it's no where near as uncomfortable. It actually feels better during the detox session.