To get your ideal weight according to your height, you have to take into consideration, your body frame as well as your age. There are many height-weight tables available at doctors clinic or over the net. As far as losing weight fast is concerned, again it depends on your constitution, your activity levels and your diet. Although the thumb rule is to go with about 3-7 kg loss per month. If you stop or reduce ANY exrcise program, it will have an impact on your weight and general health. So my advice is to stick to a program which you can sustain for your life. It will give you far more returns than just weight loss.