In "the negatives of FIRE" Nords wrote Let me sum it up this way:
Six months before quitting the job and starting early retirement, everyone worries about what they'll do all day.
Six months after FIRE, everyone wonders what the heck they were worried about.
It's an adjustment period, and everyone finds their balance. It happens faster if they've been preparing for it, but it happens.
I was told at a retirement planning session for teachers that teachers make wonderful retirees, because we are so used to planning ahead and figuring out what to do to get to our goals. I think this generalizes - if you are self-actualizing (and most on these forums are) then you should be fine. If you need some set schedule to keep you gong, you may have issues.
If you have the practical issues taken care of, finding things to do should not be an issue. But the first few months are not typical, they are recovery time.