Something anxiety sufferers really suffer with is patience, or rather the lack of it. Now I don't know what or why, but I guarantee you that at some level you are being impatient and therefore snappy, because you or someone else is expecting you to be patient and you can't for some reason, on some level.
I'll give you an example: I used to suffer from agoraphobia and got better as you did, however what I didn't realise is how impatient I could be in restaurants, shops, public places, etc. because I couldn't yet fully relax in them, the anxiety would rise subconsciously and come out as me having a really short fuse with people or the situation. When in restaurants in particular I would be impatient for the menu, impatient for the food to arrive, impatient to eat it and then impatient to get out of there, so it would do my nut in if my wife or friends would want a dessert and then order another coffee, etc. as I couldn't relax, all I wanted to do was get out of there, so then the short fuse would kick in and I would get really snappy with people because I was subconsciously getting anxious with agoraphobia rising. When I got home, like you I would be fine and all apologetic, but at the time I could be a real arsehole.
Now I didn't know any of that at the time, but slowly over time I worked out what it was and why I was doing it and began to be able to let go more in those types of situations. So I imagine that is how it is with you when you find yourself in agoraphobic inducing situations, situations that subconsciously you want to avoid, but are under pressure to relax and enjoy yourself in instead.
Now this is a pure guess of course, but whatever the actual reason I assure you that your short fuse is coming from you being impatient at some level, because you are in a situation that subconsciously you don't want to be in.