Hi Rosiemary, I don't think that's a normal match, but there are a few things you need to ask yourself, & one physiological phenom that you might not know about.
In order to keep from starving, literally, the body will slow down & reserve stores. If you were eating 3000 to 5000 calories a day, or more (very likely if you were more than 100 lbs. overweight), then suddenly dropped to 400 calories a day, your body is going to stop everything in its tracks to monitor the situation. Sometimes people who go on "starvation diets" don't lose any weight, which is also a reason why people who fast (like Gandhi) can go without food for weeks. The body won't allow it.
But that's probably not what's happening here. What are you eating? How do you know your calorie count? Are you sure?
What you should be doing is counting protein, carbohydrate & fat grams. Different doctors tell you different numbers, but my nutritionist said my protein goal was 50 to 70 grams per day. You can assume a gram is 100 calories or more in energy. So at the top, that's 700 calories a day. Most of us eat more than that, but anything under 2000 calories a day (for an obese person) will result in a weight loss. It's a simple scientific fact. You cannot eat so few calories without the body losing weight.
What most of us actually do is miscount, or we lie a little to ourselves, or we don't count a thing that should be counted, or we somehow arrest our metabolism in some other way. Whatever we do, our body is going to notice it & adjust our nutritional intake to match our caloric output--meaning, exercise or any other movement.
So the first thing you should do is make sure you write everything down. Every single crumb you eat, every ounce of water you drink. Weigh it, measure it, be hyper-aware of your eating habit. Write it down.
Usually, this is enough to reveal the problem. Almost always, we are eating more calories, or bad calories, than we're aware of.
I would say, though, that if you are actually eating so little & you're not losing at least 2 to 4 pounds a week, you really should see your doctor, or another doctor, & have your blood taken & thyroid & other levels analyzed. It's one thing to say we each lose weight at our own pace, & we are all different. It's another thing for you to eat 400 to 500 calories a day for FIVE weeks & two days, in addition to the hospitalization during that time, and not have lost at least 20 pounds.
Prepare yourself for several possible outcomes, depending on what you discover after you start logging your progress. But if you are being completely truthful & not in denial, you're not eating 1500 to 2000 calories a day, that is alarming. You really need medical intervention. That's not even remotely normal.
Of course, once you start counting, you may likely discover that you're eating too much. But if it were happening to me, I'd be waiting outside my doctor's office tomorrow morning & she would do blood tests, at the very least. If you're doing things right, there's something wrong with your metabolism. This happened to me when I developed Graves' Disease & suddenly my body went nuts. Don't ignore it BUT BE HONEST. It's easier to lose pounds by eating 25 or even 50% of the calories you were losing before. But the real fight is with your messed-up brain, which is the reason you have an eating disorder, which can lie to you & sabotage everything you want to do. WRITE IT DOWN. You can't overeat if you are honestly reducing your calories every day, & you have to lose weight if you're honestly reducing your calories every day.
But in case you're right & you've only lost a pound every week on 400-500 calories a day, there's something physically wrong & you need to see a doctor. I lost 35 pounds in my first month & 25 pounds a month the second month. After that, it was about 15 pounds a month, followed by a plateau. But it's up front that you will lose the most, so if you follow the standard pattern, you will only lose less than you're already losing as you continue on. That's not right.
Please hang out and let us know what happens next, but don't ignore it or assume it's normal.