I don't think you ever feel ready. It's a matter of are you committed to going back to work. The ready comes as you gain comfort and competence on the job. That takes experience. When I made the transition in 2006 I was terrified I wasn't ready but I really wanted to go back to work in my field. My psychiatrist promised me his complete support and increased my sessions. I took the plunge. I worked till I retired. Sure, I had relapses but I was so committed to returning to work, my psychiatrist backed me up and back to work I went. Work was like medicine for me. It gave me a sense of purpose, normalcy, competence, and financial independence. No drug my psychiatrist could prescribe would have ever given me that back after having lost it being on disability for almost 15 years.

I guess the question I'd ask is do you have good clinical support. If you don't, that's a huge impediment.