Everyone has THAT day around day 4-5, the horrible one that is the worst and it is the day before you start feeling great, the day your body is going into full Ketosis. See it as a good thing not a bad one as things will only get better after today, just get through it!
It is my second time round as well. I have actually found it easier mentally because last time (2 yrs ago) I didn't know what I was getting into, I just thought, ah heck I'll give that a go. This time I prepared myself mentally for the challange of the dreaded first week, I feel great now after being on it for over 2 weeks and I now know that I have to research properley the exact route I am going to take when it comes to refeeding. Last time I came off it, I went on an all day bender with the lads, drinking Lager and eating takeaways...BIG MISTAKE...ended up back at the beginning again, finally realised this is a chance to have a lifestyle change and retrain my bad habits.
So chin up, get through today and you know tomorrow will be a brighter day!