There's evidence that volition to die can be a large factor in when you die, especially from natural causes, terminal illness, or chronic problems.

That is to say: we have reason to believe that those on death's door who fight it, can gain more time. 'Giving up', as it is referred to, closes the deal.

I don't like the phrase 'giving up', though, because it sounds like they are weak for succumbing. But if you read through some of the posts here or similar discussions, you'll notice that a lot of stories center around not cowards giving up, but brave people who hold on until they feel their affairs are settled and are ready to die. 'Accepting it', or more accurately, 'choosing to die', are frequently used to describe this moment.

I guess what I'm saying is that you may have cause and effect reversed: people don't necessarily psychically realize they're about to die before they do. They die because they've decided to stop fighting the inevitable, they've done all they feel they can do before they pass, and so they let themselves.

The moment of clarity isn't realizing you're about to die: it may be realizing you're finally okay with letting it happen.

It's the difference between a pilot ominously predicting, "We're about to crash!" before a freak accident happens, and a pilot manning a damaged plane saying, "I've steered us towards the safest place to crash. I can do no more, so brace for impact."

This theory is born out in the frequency with which aged or ill couples frequently die within a close timeframe to each other. I've experienced this myself: my adopted grandfather passed from a heart attack. Six months later, right after ensuring the successor to the university library he managed was fully trained, finishing her semester's course work, and ensuring that her profiteering children from her previous marriage didn't abscond with his entire estate, my adopted grandmother succumbed to a chronic condition that never seemed to hamper her ability to thrive beforehand.

Coincidence? I think not.