Back in my teenage years, early 20s, my hair suffered because of my diet. I exercising a lot and really limiting the food I consumed. I believe the lack of proper nutrition is the reason my hair fell out. Thankfully it grew back.
During high school, I dropped weight quickly. Like many of you, my parents were oblivious. To this day, unless my mother has experienced it, it just can't/doesn't happen. She had easy pregnancies so mine had to be easy.. when in fact, my first was HORRIBLE.
I now have lupus and she doesn't believe it when I'm flaring.. I must have the flu, need to take my vitamins and wear glasses (I have 20/20 vision)
People handle situations differently and while we yearn for sympathy and understanding, it's not always there, sadly.

That's one reason the internet is a great thing. We can meet other people with similar experiences.
From my experience, I didn't feel worthy. My weight was the one thing I could control while the rest of my life felt out of control. Eating and exercise were all under my control. What I've learned now that control is just an illusion.
When we don't eat, we don't function well so our life goes into a downward spiral. Talk about lack of control. And what you do in high school greatly affects your adult life.
Believe that you are worthy of taking care of yourself. If you relapse, it's ok. Start over. We learn by mistakes.... pick up and start over. It's ok.
You can get better. Find your triggers. Explore your emotions. Fine someone to talk to. There's a lot of free counseling out there.
If your parents don't understand, don't talk to them about it. It'll just upset you more. One day, maybe a counselor can talk to them for you. They still love you. They just don't "get it". Hang in there. And if you need to talk, we're here.