Up to two weeks at a time of a total (water only) fast? I've done this before, but it was quite difficult to maintain in the midst of work pressures and I'm curious to know how you manage it.
I often go all day without eating while I work, and contrary to the OP and more in line with several of the other posters here I do find myself more productive, able to concentrate and focus, and feeling more energetic (I know it's counter-intuitive).
However the slightest inkling that I'm feeling worse for it, or that my productivity is beginning to slip, I'm feeling unusually tired - I'll simply eat. I'm not entirely sure losing much weight would be good for me (I don't have much to lose) and I'm not trying to take things to extremes. I just side with folk who agree that 3+ regular meals a day is not necessarily the only healthy way to do things.
Note well that this is all simply my own experience, and I'm certain people differ. I do this because I'm happy, comfortable and feel better for doing so - if you try it and don't, perhaps it isn't for you. I know I wouldn't do it if that were the case.
Drink lots of water. When you feel like you _must_ eat right now (rarely happens after day two), drink a liter of water, and go for a short 5 minute walk.
Also, add a few drops of freshly squeezed lemon juice to your water. The availability of flavor is often enough to get you through the hard 5 minutes (and after day two, it is rarely more than 5 minutes).
What I noticed is that around day 7 or so, anaerobic exercise (e.g., thai boxing) becomes very demanding and hard to keep up for more than a few minutes at a time. However, it's just as easy as always to do aerobic exercise like jogging or swimming.
Never had dizzy spells or feeling of muscle fatigue (except for anaerobic exercise) - and it was also easier to get out of bed in the morning.
However, a friend of mine noted that my body goes into a super-economic mode - that I hardly lift my feet off the ground when I walk (less than an inch on average), and that my arms seem to move quite a bit less.
I'm very surprised by the lack of muscle fatigue though. I've done fasts of 4+ days 10+ times and I always get significant muscle fatigue around that point (esp. in the hamstrings).