It may get really, really, tough. At least, the first three days were for me. Day five and six have been rather easy in comparison. In fact, today, the hunger basically disappeared.
Bellyache is right. First few days, your body will do ANYTHING to get you to eat. Headaches didn't bother me, but I did have minor "flu" symptoms.
It was the momentary hunger urges to chuck everything that kept taunting me, but since I was prepared for them, and had mustered a lot of committment, (not like once before!) I was able to strive through.
And now I'm here, having lost 12 pounds in five days! Weight loss wasn't a major incentive, but it's a wonderful side benefit! Imagine going from 184 to a (modestly predicted) 167 in the space of ten days!
You can do it! The momentary urges go away if you don't mentally assent to them. I'll be fasting all the way to Friday, and checking this board often. Post me if you need encouragement!