The problem is, the human body LOOOOOOOOVES carbs and always wants more. Like, way more than it will ever need. And with the refinement of sugar, humans figured out how to pack ALL THE CARBS into extremely tiny spaces (e.g., donuts), which do not fill the stomach. So the net result is we eat quantities of food that would be filling on a diet of leaves, nuts, and berries, but which pack exponentially higher amounts of calories and carbs than we need.
Carbs are great things. They give you energy and enable your brain to function (which can be handy). So when you stop shoving your face full of them, you feel not unlike Wile E. Coyote, standing in mid-air next to the cliff, just suddenly realizing that there's nothing holding you up.
Next comes a long fall, and a hard WHOP at the bottom. Carb withdrawal and pseudohypoglycemia, sometimes referred to as "low-carb flu," with symptoms ranging from body aches and general feeling of crumminess, to mood swings and headaches. Not everybody who moves to a lower-carb lifestyle gets it, and people with diabetes and such have it worse, because their body has a harder time switching to run off of fat and protein.
I get it. My attempts at South Beach and other such things, designed around a hardcore "carb detox" at the front generally didn't last more than two days, because it sucked so much. It didn't help that they didn't warn me that this was a thing, so I thought the misery was going to be my new "forever" and it just wasn't worth it.
This time, I'm not going cold turkey (although I'll happily eat some cold turkey). My morning mocha is sacrosanct and not going anywhere, for instance, and it's a heady brew of carbs compared to the fat and protein involved. However, I am swapping out carby staples (goodbye bagels, hello bacon) and trying to restrict most of my sugar intake to what's in the fruit I eat, with the occasional Hershey Kiss or chocolate chips in my trail mix for those "dammit I need some chocolate" moments.
But even this relatively gentle transition is enough for carb withdrawal to kick in. Wednesday was the first day I really started to feel it, although it manifested more in the form of just being "less happy and energetic than usual" rather than any sort of real discomfort. Yesterday it was there in the form of a low-grade headache and fatigue around my eyes. This morning, it's unmistakable: ringing ears, shakiness, and a vicious craving for chocolate scones. O.o
I threw the Black Dog a bone by having peanut butter on toast instead of sausage and eggs for breakfast, but I can tell that this is where it starts to get difficult. On the other hand, if I can stay the course and push through, I will be all right.
 Weaning: To remove or eliminate an item (particularly mother's milk) out of one's diet, either literally or figuratively. Weening: To think or be of an opinion. Now seldom seen except in one of Sir Joseph Porter's songs from HMS Pinafore.