I cannot imagine having this problem. I wouldn’t change my lifestyle much; I’d put the money into my or others’ space ventures, and life extension. But this is one of the reasons that lottery winners often end up blowing the money; they have no apparent purpose in life.
The self made multimillionaire types I know have all to large extent maintained the lifestyle that allowed them to earn that wealth. They have some toys but are also frugal. They have some services but also do a lot of their own housework. They do go out to eat but also do a lot of their own cooking. They stay industrious, often choosing “hobbies” in retirement that require effort and fill their days with activity.