I had a very stressful career, in litigation involving hundreds of millions of dollars, and in State Government where the businesses I was supposed to regulate had corrupted the system. I would not back down, and they tried to black ball me. I became a consultant and worked on international consulting projects sponsored by the US State Department.
All the stress affected my health. I have been fully retired for over ten years and, at age 77, would never go back to paid employment. I do some uncompensated local volunteer work in my community.
If you go back to work because you are too bored in retirement, you just never figured out how to relax and smell the roses.