In my case, when I turned 40 I realized I had mastered software engineering. I went back to school for my master's and PhD. I also took Improv Comedy lessons and joined an Improv troupe. I started a writing group and became embedded in the writing community. I am now launching a new career in publishing.
The answer, in my mind, is that you have demonstrated excellence in your field - you can probably do so in another. Go back to square one and think about what thrills you. Then (in the words of Master Suzuki) approach it with the Beginner's Mind. Take the time to immerse yourself and grow into that new realm. Become an expert.
It will take time but it will be rewarding. And, it will stretch your mind in a new direction. This new mindset will improve everything from your work situation to your personal relationships.
Remember, you were smart enough to become the best in your field - there are other fields that are less challenging that you can dominate. Pick one. Stick to it. And within a few years you will have options.