Jen--
Whether you'll be unshakably calm up to the moment of your surgery in October, or as Nicole suggests may happen, you find yourself running a gamut of emotions as you process the news--either is YOUR way of dealing with this. Of all the responses I got (none were encouragement to "stay strong", as you have gotten--I think most were dropped jaws!), the most incredibly helpful came from my wise and wonderful older sis. She said "whatever you feel, it's OK; you're allowed to feel whatever you do about this."
Before she said that, I think I was in shock--afterward, I let myself have a good cry or two, a brief freakout, and then was, over time, able to get back to being calm (and it didn't seem "strange" anymore...)
So, whatever you feel--it's OK! (But, however it goes, I think you should use the time between now and October to be very nice to yourself!)
Carrie