I think the thing that ultimately got me over the OMY hump was not viewing my decision to quit as the FINAL choice, never to be undone. If, instead, you just look at quitting as the current choice that makes sense for your life right now, based on already reaching a comfortable FI amount, then you can leave knowing that you can always return to work. Even if you can't go back into your exact job with your previous employer, you can always do SOMETHING to earn some income. Who knows, you might want to one day return to some kind of work or do some "side gig" to earn some money here and there.
I had/have to get past some serious golden handcuffs if I stayed OMY: high earnings, a much-increased pension, inexpensive healthcare for life, etc., if only I stayed a few more years. So, as a bit of a middle road and insurance policy, I took a sabbatical/one year leave of absence (unpaid), but with my likely intention not to return unless I found early retirement less than I dreamed, or if there was a major market downturn (bad sequencing). My employer holds my job open for me for one year. So far, ER has been everything I dreamed and more.
That little bit of a safety net gave me the confidence to leave and "see how it goes" for one year, instead of staying at a job I was getting sick of for OMY. But really, it's not the guarantee of returning to a job that matters: it's frame of mind that you can always choose what makes sense for you later, even if that's returning to work.
So even if you can't arrange an unpaid leave of absence, you can just tell yourself that you'll quit for a year or three and see how it goes. If you find that you're spending too much, or markets have tanked, or you're unhappy with retired life, you can make some adjustments or pursue some passion of yours to make some $. And you don't need to earn a ton of money once you're FI -- you just need a little earnings to make up whatever shortfall you've encountered.
One thing I discovered after quitting is that I really enjoyed making wood furniture, and it's easy. After comparing some things I've built to the stuff being sold in high-end stores like Pottery Barn and Restoration Hardware, I feel I could pretty easily sell stuff for half of what they charge and make a relative killing. $500 for a nightstand??? Come on!! So if I wanted to pick up some extra $, I could do it in a way that's enjoyable to me and doesn't have me sitting at a desk all day. So far I've had zero desire to earn one penny doing work, but maybe that will change in the future.
In my case, even though the markets have been pretty tame since I ER'ed last November, I'm finding our net worth is still increasing pretty substantially (just as MMM promised, haha!!). That's been further peace of mind that we can live comfortably within our budget, all while still building a larger safety net against future downturns. I'll bet you will discover the same thing.
If you need any other push not to wait too long: You're not getting any younger ;-) Don't be like several colleagues of mine who have been taken away from their desks by ambulance after suffering heart attacks or a stroke. Or many that I saw literally limping to and from work, hunched over, in their old age. Or many, many of them that officially retire on Friday at age 60, drawing large pensions, and are back on Monday as contractors to earn even more. What is that about?
So why not give it a try, temporarily, and see how it goes?