I'm very overweight. How I envy you . . .

Seriously now, losing that much weight in so few days means that you're losing mostly water, not fat or muscle. Not really a problem, if not happening in extremely hot climates, where it could lead to dehydration and low blood pressure which, in extremis, can bring you to faint.

You can easily prevents it drinking more liquids, preferably not pure water, but liquids with potassium and electrolytes, such as Gatorade or similar.