These 2 quotes stuck out to me (just my personal experience though):
Some days I can do it with grace and dignity, other days I’m literally clawing my way through - think positive “every day as my last” stuff is just beyond me on those days. I can’t live with that kind of intensity and not loose my mind.
This sounds like kinda a form of OCD to me... (mildly) obsessing over the thought "what if this is the last moment we share" and then needing to act accordingly...
For me experentially I find it quite the opposite: there is absolutely no conscious 'thought' about the reality it could be anyone's last day, or "what if's". I'd describe it more as many points of performance, wherein then that conscious thought comes in to awareness.. much like holding your tongue in an argument, recognizing this could affect the future. Recognizing if this were your last conversation either one of you would be left on that note. I see it as sort of a nearly constant physical and emotional Emergency Preparedness. Not out of choice whatsoever but out of a lifetime of experience, and requirement to do it. 'Knowing' everything could change in a minute.
I also think it has nothing to do with control of the situation or superstition or random fears, but more like controlling the only part possible: consideration (and attempt) to provide the best life for others and least regrets for self. In the event of worse-case-scenario. But it is also very different from assuming the worst.
I think the real problem comes because it is like a point of performance, but when all other points past are not remembered.
I saw my dad do it too; it was the same reason he could be thoroughly enjoying himself one moment, and pacing the floor 3 hours later when my mom was delayed. Or bolting across a parking lot in seconds flat when a stranger collapsed on a hot day. He was there before anyone would have seen her go down, and most would have assumed she likely just fainted.
I also think living knowing today may be your (or other's) last is just true, that can actually contribute to making a better day, not sweating the small stuff, learning to stop and smell the roses, looking for opportunities to give more and love more. I think the key words are 'may be'. But not as in putting more pressure on, as in being grateful for what is there now.