Hyperventilating when anxious, is this a panic attack?

No it is a symptom: When we get anxious we start breathing fast so we disturb our blood electrolytes think of us like a bag if running chemicals which are regulated by breathing. We breathe in beautiful oxygen and it goes in lungs and carbon dioixide comes out but after a complicated process of chemical exchange in lungs blood electrolytes keep us calm if we get anxious and start fast breathing the whole cycle messes.

Panic: It is a symptom commonly seen during panic attacks, along with other symptoms such as apprehension, chest pain, shortness of breath, trembling, fainting, etc.