Kitt has put that really well. You can suffer from panic attacks but not have a "nervous breakdown". That terminology (I'm not a professional - don't quote me!) was used more in the last century to describe many manifestations of mental disorder.
At that time there was not as much knowledge of the difference between severe mental disorders such as schizophrenia, and our modern understanding of depression, anxiety, OCD PTSD etc. It was the generalised term used for someone who needed to be admitted to hospital/institution for a mental health issue (also not a word used much then).
I hope I haven't confused you. Just wanted to add my 2c