Technically, I'm not retired. I'm long term unemployed!
That's a good description! As I'm fond of saying, the only difference between retirement and unemployment, is that the retiree has more money.
The first time that my career peremptorily collapsed, I was already financially independent, by conventional definitions. My material standard of living didn't change, whether there was an incoming paycheck, or not. But then one had to reckon with the psychological absence of that paycheck, etc.; plus, no longer being able to add to my portfolio. I couldn't abide that, and so, made every effort to return to work. The process repeated itself some years later.
The OP's question is wisely delimited, by age. There is, I think, something magical around age 60, plus or minus. Sure, that's "early" retirement in the sense of Medicare or Social Security, but it's not distantly early. Now try the same, some dozen or score years earlier... very different psychology, very different pressures and sense of self and sense of "enoughness"... even if one is comfortably FI.
Successful retirees, retire on their own terms. Even if the sudden withdrawal of office-dynamics at first is jarring, one gets used to it, and grows to enjoy it, if one's exit was planned, voluntary and deliberate. And if not... I dare say, not.
