There is an element of truth to the above. I know on multi sector days your brain can almost go into autopilot mode itself. Not that you are not functioning correctly but in some ways a more relaxed attitude and relaxed to everything
In some ways you can connect it to the second wind on running a marathon that getting to the point that you cannot run any further you go through that into something else more like running on automation
I had that on a Europe USA ferry which involved a very long day arriving in Dallas late at night.
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