If I were you, I'd still see a doctor and/or your counselor or shrink. You're not out of the woods yet.
Temporary dehydration? You have no idea of how your liver is functioning and the electrolyte imbalance that could be causing thyroid and/or heart issues.
Your words indicate that this might be a chronic issue due to eating disorder.
Do NOT self-diagnose. Not now..not ever.
I don't mean to sound harsh...but you have some serious health issues
going on..besides this blood chemistry issue.
Your title is "why am I this sick?" You know damned well why!