At first, my husband wasn't understanding, because he doesn't like the idea of taking medications and such. He also had the "just get over it" mentality. I think it's just because he didn't 'get' anxiety or what it does. I've been very open with my experience with my psychiatrist, therapist, medications, etc. I tried to hide my for a really long time because I felt bad about it and so my husband never really saw it. I find that it's important to share how you are feeling with your spouse and let them into your world. They won't understand until they know the extent of it and how it affects you.
After that, if your spouse is still not supportive, I would be concerned, because it will be harder for you to feel better without that support system!
As for how to tell him, just be frank. Describe your physical/mental symptoms and let him know when they come up. I'm sure he will want to help you in any way he can. :)