My wife’s brother passed away on January, at 45, from a still unknown cause. No known health issues, no vices, ran every single day, was former military and current electrical engineer, and just did not wake up after feeling a little sick the night before. We figure that it was likely a cardiac event, but won’t know until the coroner turns over his findings.

My wife and her sister are is very experienced RNs, and have gone over every little bit of evidence, as we wait on the autopsy, but all we can do is accept that it was his time and part of God’s plan. Our family is all very active, and have overcome so many major health trials with my Crohn’s and my Father in Law’s liver transplant a decade ago, but losing the healthiest male in the family, was definitely a hit to our view of mortality, even as our faith remains unfaltered.
As you mentioned, we now are seeing the small trivial issues for what they are, small. We are grasping for every bit of our faith, and trying to understand why he needed to be there, even more than with his wife and 4 children, 1 who is about to turn his mission papers in. It just comes down to feeling loved ones you love them, NOW, not later. Let go of the past hurt feelings and make new bonds with those you once loved but separated from out of anger. It is not hard to humble yourself when you were reminded how quickly the opportunity to reconcile, is taken from you.
I pray that your family finds peace and that your sister continues to find the faith, strength, and courage to keep fighting and raising their children. My heart goes out to her, as I watch my own sister in law put on a brave face, just trying to get through each hour, doing the job of 2. I pray she’s lifted each night by God’s love, and reminded that this life is but a blip on the spectrum of Eternity, and they will be together much longer than mortally separated. That Family Reunion in Heaven will be joyous and beautiful.