Thank you for reaching out and sharing this with us. I'm sorry that you've been having these panic attacks but at the same time I'm really glad your parents were supportive and your GP too.
The irony isn't lost on me on you being a Greys Anatomy fan and worried about medical conditions :) It can be the best show but seriously the worst in making us worry.
To answer your question though, that depends on what things she tested. Thyroid changes can cause anxiety, as can other things - if you did have a thyroid problem more than likely it would probably just be a script (medication) of some sort. Your GP is really going to know more, but there's so so many simple solutions now that if there was something not quite right with the bloods, it's highly likely there's an easy explanation.
If not- your GP might want to talk to you about how you can manage your panic attacks. Typically that's a therapist but there are lots of self-help options to try. It's okay too to ask them all the questions - while you might be the patient you can also be in charge of your treatment.
Hope this helps!