I was approved for SSI within 4 months on the first try, and am receiving the maximum amount ($674 - my state does not have a bonus). In the US, agoraphobia is on the official "if you have any of these you are indeed disabled" list. The only thing you have to do is prove you have it.
I applied based on both bipolar (also on the list) and agoraphobia, and I have a paper trail 10 years long which involves diagnoses by 6 different doctors over the years and 2 hospitalizations. I've been on about 10+ different meds over the years and listed all of them on my application. I did not qualify for SSDI because I haven't worked enough. I currently see both a therapist and psychiatrist. My psychiatrist barely knows me, but my therapist was very supportive and understanding through the application process and I know she wrote all the right words on her paperwork.
All I can say is, if you are suffering from this, make sure you see a doctor/therapist about it, just to get your name and diagnosis in the system. Make sure you build a paper trail. List any doctor on your app that would be likely to vouch for your condition, even if that's not why you saw them. Make sure you can list all the names and dates of medications you've taken for anxiety. Be extremely honest and upfront about everything, even if it's embarrassing and makes you feel like crap.
You will probably find, as I did, that it is horribly demoralizing having to list out exactly how you fail at life in excruciating detail. They sent me a long questionnaire to fill out detailing exactly how often I bathe, what (if any) chores I am able to perform, what my diet is like, etc. I had to forcibly switch off my "Everything's fine, everything's great" routine that I keep up for people and tell everything exactly as it is. Like, gee, thanks for asking, I indeed only shower like once or twice a week, I have trouble getting out of bed most days, I'm always exhausted, I eat like 1/3 the amount I should because it's a huge emotional drain just preparing food and I rarely buy groceries, I live in a garbage dump because taking out the trash is terrifying, my mail lady hates me because I only check the mailbox once a week, etc.
I also made sure to write in the Additional Comments section that it is not easy for me to ask for assistance and I am not just trying to collect free cash and live on easy street. I'm legitimately having a very hard time and need some help paying my bills while I try and work on getting better. I told them that this is the beginning and not the end; that I will keep going to therapy, and that when the stress of "Oh god how can I afford to live" is out of the way and I'm on steady ground, the real work can begin.
Also, I'm serious: be honest about everything, especially money. They do check and they will ask questions. If they catch you in a lie, there will be consequences. And the truth is probably harrowing enough as it is, so you really do not need to embellish. If you really do have agoraphobia and have lived with it for years, you have a real condition and do need help. The government recognizes that and will help you as long as you can prove to them how you live. You don't need to make it sound worse than it is. It's already bad enough that you (and I) can't leave the house. How much worse could it really be, you know?
Good luck to everyone. If anyone has any questions about the process or my experience applying, I'd be happy to help.
