I'm glad you got the courage to weigh in. Now you know where you're starting from, and you're only going down from here.
The freaking out if you lost weight really isn't that nuts, but it does have an emotional component. Here's my take on it, which I learned because I had the same problem. Although you hate it, you're comfortable with your fat and it protects you, and when you see yourself letting go of that protection, it can be quite scary. In fact, you can get quite panicky about it. I hope that you'll post here or talk to someone when you get those feelings because they can be overwhelming. I'm not trying to scare you, but hopefully let you know that others have been there, too, and we've still managed to succeed (or partially succeed as in my case) on this journey.
Women who behave rarely make history.