Overactive:
palpitations
sweatting
anxiety
excess mucous in throat etc
appetite can vary to being non-existant to excessive
weight loss
lack of periods
hair loss
I had the palpitations/anxiety/loss of appetite and weight loss in my last year at school and I honestly thought that it was just stress due to exams and that I needed to get a grip so didn't tell anyone about it.
It wasn't until a couple of years later that my periods stopped and my hair started to fall out that I went to the gp, and my levels were sky-high. At this point my appetite had also increased to a massive level and I was eating all the time. The consultant then said that the symptoms I'd experienced a couple of years previous were most likely the start of the problem...
If only I could still lose weight that quickly though