I was doing something similar, two meals a day instead of your one, and then GERD occurred and fucked me really good for six months. My doctor told me that consuming all food in one or two sittings is the worst thing you can do long term because you end-up overfilling your stomach with food and given enough time acid will start escaping upwards. Of course everyone's organism is unique, I'm just expressing my concerns from my experience with similar dietary habits.
Usual advice, as far as I know, is to lose max 1% of body weight per week. Please ask your doctor if 3kg/week is fine.
3 days is not a long enough time to see a trend, that's water weight...
There is literature out there that intermittent fasting is an effective tool in weight loss. I think the jury is out as to the metabolic effects, but just not snacking away all day helps you lose weight.
I suspect that my body was just "normalising" and after a certain threshold it would probably have become harder to start losing weight without exercising. After I traveled for work my diet got totally screwed up and I went back to 100kg. I'm now on day 3 of the same diet and am currently at 98.5kg. As for my mood, well-being etc, nothing's really changed except for the mild hunger pangs (which I got used to quickly) and that I seem to get drunk quicker when I drink.
This is just a personal anecdote. Don't take it as medical advice of any sort.