The condition agoraphobia is indeed a severe mental illness and can prevent people from living a good life and prevent the person with agoraphobia from leaving their homes to work jobs or do things other people would be doing.
Agoraphobia is an extreme avoidance of situations and places that can cause panic to the person with Agoraphobia.
When you have agoraphobia which is considered to be a severe mental health issue you will see a mental health professional who will discuss some things with you to determine if you have agoraphobia.
The agoraphobia may not be determined in just one appointment but instead may take several appointments and visits and discussions with a mental health professional before they actually diagnose you with Agoraphobia.
If you do have agoraphobia then you will have to have extreme fear of things such as public transportation including things such as a bus or plane.
Or being in an open space, such as a parking lot, bridge or large mall or being in an enclosed space, such as a movie theater, meeting room etc.
People with agoraphobia can also have a very hard time leaving their house and going in public so you might be able to get disability payments if you cannot function properly to get out to work around people to make a living.