About Failing Fasting

I am a horrible faster. Truly. I try and take on these big goals with all these great intentions and expect the heavens to open . . . for about 2 hours. Then, my body starts shaking, I crave things I never eat, I feel like I am going to die and no amount of motivative speech can help me. I have even been known to seek out food during a fast that I wouldn't normally, in an effort to apparently rebel against the spiritual discipline.
Take today for instance. I was only going to fast for part of the day. Part of the day turned into a smaller part - just the morning. That turned into just a meal - lunch. Now it is 11:33 and I am wondering how SOON after "lunch" the fast could possibly end. . . even though I just ate half a muffin. (One of the best muffins I have ever had, actually. If ever in Muizenberg go to the Artisian Organic Bakery - but that's not the point).
I once did a really long fast. Realizing I may "lose my reward" by sharing this, I think it is worth the story. This fast lasted 40 days, and it is said that the last couple weeks were "questionable" because I ate mashed potatoes (my favorite food), cheesecake shakes (a beautiful invention of my brother-in-law), and various kinds of blended soup. However, living off this limited menu was perfectly hard enough to be considered fast worthy.
Before I started my lental withholding I made a book of goals and verses and general things that would keep me focused and pressing on. I also had a group of people praying for me every day and would send out daily updates on how I felt and how they could pray. But one thing in particular marked this long fast that I am lacking today: Grace.
I had LOADS of grace during the long fast of '05. I felt like I was held up the whole time - that God wanted me to succeed because he called me to it.
Today, I am fasting out of my own weak strength, and that isn't good for anyone, or creating any treasure in heaven. Actually, I am just failing. Where is the other half of that muffin????