Pony at the barn where my kid rides, dropped and struggled briefly before dieing. Approx age was 12, healthy, grade pony. Happened almost a year ago.
I know of a 30+ pony who went to sleep and never got up. (That is how I want to go!) Happened almost a year ago.
And I know of a TB mare, young, 6-7ish, found in her stall that morning with major issues… through out the day vet attended her and owner was there. That night, she went down again and had a seizure and was gone. Necropsy done to rule out disease (vets were thinking neuro rhino) and discovered she had had strokes and an aneurysm. Happened 3-4 years ago. (That was the worst 2 days for me… as barn manager.)
I also know of a horse that should have died, but didn’t! Fine that morning, early that afternoon was covered in welts, blind in both eyes, jaundice, and shocky. Blood work said liver and organ failure. By the end of day 3 his eye sight was back and the jaundice was going away, welts were gone, and new blood work showed heavy infection. (That was a turbulent 6 months saving him!) But I have this feeling, that if it had happened during the night, I would have found a dead horse that morning.