You say:
>not being in harmony...

Being in harmony is being with what is, just the way it is.
>My mind says...

No matter what the mind tries to tell us, life starts now. Always does.

>as I missed the opportunity back then…

That’s what the mind tells you, but you do not remember accurately the
circumstance at that time, or just think you do?
Did you do the best possible under the circumstances at that time?
That’s all you can do - the best possible under the circumstances of the
time.

If you do that, every moment, there will never be any regrets.

>My system still contracts when my mind goes into the projected nuthouse
>which I know isn't true…

Until you start to realise that you are not your system, you will keep
identifying with the lesser intelligent part of yourself.
Bodies contract; minds go/live in turmoil; emotions get/are disturbed.

Who knows that? The body/mind/emotion? No, there is something else.
Until you start to at least make space for the possibility that you have
another part of yourself, that is not disturbed by these things, you will
continue to be in turmoil.

If it is necessary, it is amazing under what handicaps we can perform.
I used to have migraines that were not only painful, but rendered me
almost blind. Yet when leading groups, and not saying anything about it,
no one noticed. Just have to experiment with disconnecting from any part
of your system that you do not need in that very moment.

The next thing is - learning to be with every moment, just as it is.
That may include regrets, and aspirations,yet the only important thing is
-
is there anything you can do about it in this moment?
If so, do it; if not, disconnect, and be in the moment, just as it is.