My first feelings of relief were when I had a lawyer set up, I had the necessary paperwork in place, I felt a huge weight off of my shoulders as I knew I had help and support. I saw my counselor regularly. And, the decison was made. I almost felt like I was floating compared to the initial heaviness.
From then, on there were ups and downs, but nothing quite as severe as the initial shock and making the decision to do it. Have you started the process yet? Hang in there, it will get better.