So, as you're probably sick to death of hearing about, I switched to flat shoes. Mizuno Wave Universe 3, specifically, which is a racing flat made for 1,000 to I'd say 5,000 meter racing.
Changed everything. Changed my running form, I should say, but "everything" fell in line right behind that. All those issues melted away and have, to this day, never recurred, and now I'm able to run as much as I want, train as hard as I want, and so forth, with no pain. It's amazing really. It's personal success stories like this which have made it such a trend. For good reason, in my case. For me, there's no going back, it's not even a question.
What shoes do you wear for marathon training?
p.s. Are those exact flats still purchasable anywhere? Can't find them online (size 11').
The racing flats I mentioned are designed for racing, definitely. But the idea is that you wear them for all road runs, fast or slow, as a means to changing your running form.
You can probably get Wave Universe on Amazon.
I never did marathons, but I consistently ran 4miles a day ~7:30min/mile pace for 2 years rarely missing a day.
Never got sick and definitely had no trouble sleeping, but I would get knee pain, leg pain and foot pain randomly that wouldn't go away. Mentally things seemed good, but I did notice being more tired in general and unless you run early in the morning it does take up a decent amount of time.