erm i dunno but if you follow the plan to the letter it should just happen, i had hardly any symptoms didnt feel ill didnt get headache infact i got ridiculously hyper but i must be there because im loosing weight (is that the right way of spelling loosing?)
If you are sticking to the program and not cheating then you'll be in ketosis by about day 3 (I think) Just make sure you are drinking plenty to wash the little blighters out!