Change is inevitable. No matter how much we want things to stay or go back to how they were, they never are. So why grieve over the past that can never return.
Yes, you were healthy and vibrant a year ago and now you have a chronic illness where you feel like crap most of the time. Focus on the fact that you are alive. I know it isn’t easy, but a different life is what you are dealing with now. Try to find the best in everything and it will make it easier.