He was also "unbelievably energetic" and his health was "very robust," according to his close friend and co-author, Bryan Garner, who was "stunned and shocked" at his friend's death. Garner had just spent 14 hours a day with him during a nearly two-week Asian trip that ended the week before the hunting trip. Source: The National Law Journal. I'm linking to the story through smu.edu since the Law Journal has a paywall. http://www.smu.edu/News/2016/bryan-garner-lawjournal-15feb2016
Please cite a source for Scalia being diabetic.
According to his doctor his health was so poor that he couldn't recommend Justice Scalia undergo surgery to repair his shoulder. That was this week.