I have agoraphobia with Panic disorder. As agoraphobia literally means fear of the marketplace it is a bit of a misnomer.
As opposed to anxiety and people thinking the two are almost the same thing they are about the same as some one poking you in the chest in and someone firing a shotgun into your chest from a foot away.
Panic means fatal fear. It came about as a word in the time of the Ancient Greeks. Most of the Greek gods were handsome and perfectly built. There were two notable exceptions The God of Fire who had been born with a crippled leg and Zeus threw him from Olympus. He built his forge in Volcanoes and made most of the gadgets which gave his brothers and sisters their powers. He even made Zeus his thunderbolts.
The other was Pan god of the Forest. Those who worshiped him were called Pagans and he was half man half goat a say tar. However he was said to be exceedingly ugly. So much so that to suddenly see if one would die of fright. This explanation was given for anyone who died in the woods with a look of terror on their faces. They were said to have died of Panic due to seeing the god Pan.
When I was 4 as my family was leaving church the minister asked my Grandparents would do him do him a favor and take some groceries to a lady who could not go out herself. Being 4 I asked my parents if I could go and all said it might be a good idea. The lady was an older lady older than my grandparents and very nice. I remember her home was immaculate and hand made dollies covered everything. I was told she couldn't go out herself. After we left I asked my Grandparents why. They told me she had not been able to go out since her husband had been killed in the war. Whenever she tried she had to be rushed to hospital for a bad heart. I said "Wow the war was over 10 years ago. " ( Not bright my Grandfather had served and in 59 there were events taking place to celebrate ten years since the wars end." My Grandmother took my hand knelt down and said " No Sidney, The First World War ". It was first experience with what now know is agoraphobia. Since she had the heart problem it today would have had the words Panic Disorder added to it. I have not idea by why monetary means she was supported 4 year old boys don't think of such things.
Panic attacks can happen because of some trigger being activated. ( My Mother was robbed at shotgun point and afterwards could not go were there were groups of older teens to some stage even now roughly 20 years later ) PTSD can manifest itself as panic disorder. Sometimes nothing seems to trigger it it just goes off. People tend to avoid where the attacks took places until at it's worst you are housebound. At present my world consists of a few blocks. To make matters worse I had to move here to move here to live with my Mother when I could no longer afford to live in the "retirement" home I was in as I had only my disability. My work pension had not kicked in till the 29th year employed was done. I had used up my sick time and they were good enough to keep me on the rolls a couple more weeks so I would qualify. The 30 years of paying into insurance didn't help as the insurance company refused to cover so called mental lionesses.
Anxiety disorders can rage from social anxiety disorder being unable to be in a crowd to stage fright which is the most common to an almost limitless variety of phobias.
Anxiety disorders are similar in ways to Panic disorders but are vastly different in degree. One will raise your heart rate the other if not got to in time explode your heart or more likely cause a stroke. The extremely high blood pressure combined with the high pulse can break free plaque from an artery wall and send it to the brain or elsewhere. As an example in terms of numbers I have shown up in hospital and had a BP of 220 over 180 and a pulse over 290. that after being given meds in the ambulance. That I am still alive is very unusual.
For most getting upset can be unpleasant for people like me it may well be fatal.