I'll chime in with a "me too" - I agree with all the previous posters also. It's a very common reaction. Unless you start progressing rapidly (an unlikely event), you'll most likely calm down within 6 months of being diagnosed (of course, no guarantees on that timing
It really sucks when you first have to mentally readjust your view of your life, self, family, career, etc. It's going to take some time for most people. I don't think I admitted to myself that I really had MS for about 6 months. But if you're like most of us, you'll progress slowly if at all and realize that you may never endure most of what you are fearing now.
The best thing that happened to me early on (and I don't necessarily recommend this) is that I went to an event for people with ALS (I know someone who ran it). After meeting all those people with ALS, it really pulled my MS into perspective for me. I was really feeling sorry for myself because I was comparing the "old me" to the "new and unimproved me." Once I compared myself to others with a much worse disorder and seeing how they were dealing with it, I was truly humbled.
This isn't to say that a diagnosis of MS is a good thing! But it will take some time to get your perspective back. You've just had a bomb dropped on your life. The vast majority of folks with MS I know recover from that quite well. It just takes time.
Seeking out others (like you're doing) in a similar situation was very helpful to me also.