How to know if it's a panic attack?

This will probably sound stupid, but here goes...

I have had this feeling many times, but I've never known for sure whether or not it was a panic attack or just bad anxiety. When it happens, I get chills, my teeth chatter, it's like my whole body shivers (ESPECIALLY my hands), I get super nauseous, my stomach feels like it's flipping over and over, there are tingling feelings in my arms/legs, and my head feels hot inside and I can't think very clearly. It often happens during exams, and my brain will like lock on to the sound of the clock ticking and I won't be able to tune it out. It's like I will focus more on the sound and nothing else, and it takes me a while to settle down enough to continue what I'm doing. My handwriting becomes almost illegible and I feel frozen in place. It feels like I'm not even breathing. I have bombed quizzes before because of this, and would do anything to get rid of it. I'm lucky I usually stay mostly functional even when its happening, and people can't seem to tell really, except that I have to stay completely silent. This feeling also happens when I drive, which I no longer do due to this reaction. Is this what an anxiety attack feels like, and is there a way to calm down before it really gets going?

It sounds like a panic or anxiety attack yes. There's coping strategies you can learn to avoid triggers for them or recognize when they're coming so you can work on calming yourself. I would suggest you seek therapy if you're not already! It would really help you deal with the anxiety.