Michael Moseley did a lot of research into it, and concluded that rapid weight loss, was actually a lot better than "slow and steady" (despite the fact that slow and steady is usually recommended). His research and findings were really enlightening actually, and very convincing - there's a lot of information on it in his "Fast 800" book. But I imagine there's somewhere online which summarises it more succinctly, if you can't be bothered with a whole book.
I remember in one bit, he did a full three-day fast, where he had nothing at all but tea without milk. They took a load of measures of his body before and after (blood sugar, markers of inflammation, something else which showed risk of cancer I think too). His body was MUCH healthier AFTER the fast. If you do a very calorie restricted diet, it also triggers "autophagy", which if you don't already know, is when your body essentially eats any damaged cells. It's really good for you, when this happens. Obviously it's not for everyone, but the research shows that rapid weightloss, isn't necessarily a bad thing.
That said, I don't know what the implications would be, if you did this every day for weeks or months. I'm sure it was in the book, but as it wasn't relevant to me, I can't quite remember what it said!
Also, I think with extreme calorie restriction, you are likely to lose a lot of hair. It will thicken up again once you are eating properly. For me, it would be worth a bit of hair thinning to be healthier, but I imagine that's not the same for everyone.
I've also read that you are more likely to lose muscle (and thereby reduce your metabolism), if you lose weight quickly. I'd focus on eating fewer carbs, and more fat and especially protein, if you carry on as you are.
Lastly, I've heard that the more rapid the weight loss, the more likely you are to get loose skin. I'm not sure on the truth of this, long term. Obviously it will take a person's skin longer to "catch up", and might be looser during this period. But presumably if your skin has the capacity to shrink 20% over all, would the time frame make a difference? I don't know. And an individual might not care about looser skin, if their joints or whatever felt better quicker. Again, it will vary person to person.
Just realised what an essay this is, sorry! I think it's a really interesting topic 😂