Switching your intake to a low-carb-high-fat diet involves a grace period a week or so. This is to allow the body to "reshape" itself to use the fat as an energy source instead of the previous intake of carbonhydrates.
Symptoms of switching away from carbs to fat include; fatigue, dizzyness, high irritability and headache.
"After only a few days on the high-fat diet, the rats performed 30 percent worse on the treadmill. After five days of testing, the treadmill performance of the rats eating fatty foods had declined by half."
Any bells? So, nothing previously unknown to the lowcarbers here.
Personally, I tried the lowcarb-highfat diet about half a year ago, and actually did lose a few kilos, but the most interesting change for me was that I felt more awake, my stomach stopped producing funny amounts of gas, and never ever felt hungry. I got tired of it after a while though - I kinda missed the occasional potato and pasta - so I've taken back the lost kilos again. These days I just don't shun fat and avoid sugary stuff. Both me and my previously upset stomach feels great now.