Ohh, I bet you're excited!!
You really don't forget. You will definitely need to strengthen some unused riding muscles and be reminded here and there of a few things, but for the most part, at least I found, it will all come back to you when you're in the saddle. I was away from horses from the age of 14 to 27, and when I saddled up for the first time it was second nature to me. It was very strange to just "know" and "do" without thinking but it was like I'd never dismounted. :) Of course, the next day after that first ride i was pretty much stuck on the couch because of muscle stiffness, ha ha, but I was so happy about owning a horse again the pain wasn't going to get me down.
Good luck, have fun!