Most people seem to experience some kind of symptoms from the fat burning switch...it's usually quite pronounced but if you are sticking to the diet and are losing you may have passed through the barrier : )
I have read that some people do however take a bit longer than the three to five, so don't be alarmed if you do feel grotty...and good luck
I only got a really mild version - but a friend who has a really sweet tooth suffered badly... I've also never really drunk strong coffee/tea ... I think abstaining from caffeine and sugar must play a big part.
My partner started feeling fluey on day 3 and still does now (day 6), whereas I'm yet to feel any major difference. He, however, could happily have lived on a diet of sweets, chocs, ice-cream and coffee previously so as Alpaca said, maybe the withdrawals match the severity of the original 'habit', if you see what I mean?!
Good luck xxx
Hope that you have a flu free induction. Agree that it seems to be proportional to ones carb addiction. I havent been that ill for a while and the good news is i dont want to be again- helps keep me on the straight and narrow