I’m so sorry for your loss. It does happen and sometimes much slower. I contracted the flu approximately 10 years ago. My immune system began attacking my lungs. After several diagnoses of pheumonia over just a couple of months, they accidentally caught a glimpse of the bottom of my lungs in a CTscan while testing for something else. They were all scarred up. Thank God for steroids, that is what is keeping me alive today. BTW, I’m only 48 now.
In the late 70’s, a co-worker went home with the flu. When he didn’t show up for work the following day, his friend went to check on him. He had died in his recliner, sitting half-reclined. His lungs had filled with fluid and he suffocated.
Prayers for Big Black Dog, his family, and all who loved the deceased. May God ease your suffering. I’m sure your brother will find a place reserved in Heaven at our Father’s side.