When you go onto a diet particularly an extreme one, your body gets rid of a lot of water. This is what your initial weight loss was mostly due to. When your new diet stabilises your body will store more water and your weight will go back to near where you started. You will start to lose weight again when you water content stabilises. You cannot expect to lose more than 2lb per week as you would have to go on a starvation diet. To put your initial weight loss in context, if you had lost 8lb of fat in 4 days and hadn't eaten at all, you would have had to run about 75 miles each of the 4 days to burn up that amount of fat, obviously implausible. If you halve your normal calorie intake, say 2000 calories per day to 1000, you can expect to lose 1-1.5 lb per week. If you starve yourself then only 2-3 lb per week. A clever thing to do is not to eat after 6 in the evening this means that most of the food you eat gets burned up before you go to bed and doesn't get turned into fat overnight as it would if you ate later.