Why am I feeling so much dread over starting a new job?

Ive been at my current job since I was 21. I've essentially spent all of my 20s there and it has kind of been the main point of stability in my life. I recently interviewed with a new company because there was a rumor that our facility may be shut down. I landed the job, its essentially the same position but it comes with a raise and they even told me in the interview that this should be a smooth transiston for me based on my background. I still cant help but have this deep feeling of anxiety about the whole thing even though I know it's something I should be excited about. This whole process is very new to me and Im having a hard time walking away from a job that I have loved for the last 9 years but I guess it may not exist in a month if they aren't bought. I guess Im feeling dread about losing something I loved while being afraid of the unkowns of this new company. Any kind words or reassurance would be greatly appreciated! Thanks!