Hi there ~
I understand your concern. Your weight can vary during the time of the day as well as during each day. This is due to what is called as water logging. I hope you are not using any diuretics, unintentionally. If that is the case then it would explain the weight loss
. There is no way you could have lost mass by fasting for one day, i.e. 4.6 lbs in 4 days. I also think that eating, having a full bladder or bowels may make your weight artificially go up higher. I hope this explanation helps.
Please consult a nutritionist as well as an exercise specialist for weight loss questions. I hope this helps.
Take care and have a lovely day!