If you've ever heard of the 'The Chimp Paradox: The Mind Management Programme to Help You Achieve Success, Confidence and Happiness' by Prof Steve Peters, I recommend it as way to understand anxiety and phobias. He's the person who has helped a lot of British Olympic athletes win medals, amongst others.
There are other books about the subject, but this just happens to be the one I've picked up
He explains that we have two ways in which our brains work; the emotional chimp and the rational human. The whole principle is about how your emotional chimp can take over and needs to be managed.
Its really good as it explains why the irrational part of your brain overrules the logical bit in a really good way. Just understanding WHY you are acting in a particular way and you are not 'crazy' just normal. It was a massive stepping stone for me. No doctors necessary.
If you are struggling to leave the house or don't want to face a therapist or doctor, it could help or at least be a stepping stone to that in the future.
What have you got to loose apart from about £9 (or see if you can get down the library or get one second hand)?