First of all, it is impossible to simply reduce fat. The process of losing fat is accompanied by the loss of water and muscle. So if you are 6 kg of fat, water and muscle will basically exceed 10kg. From the point of view of health and nutrition, the normal weight loss rate should be 1% of your weight loss every week, which is 0.5- 1kg. So, I think your physical exhaustion is back to the limit.

Therefore, under normal circumstances, it is possible to have a weight change of 2-3 kg in the fitness class, but most of them are water. With the end of fitness, eating and drinking regularly, weight will naturally recover. Moreover, the result of rapid fat reduction is irreversible relaxation of the skin, which can only be achieved through surgery. So slowly lose fat.