A friend of mine suffered a head injury about 15 years ago. Since then he had been having seizures caused by damage to parts of his brain. As they became worse he had to forfeit his drivers licence and began having a hard time executing basic necessities of life. I'd help him with shopping and whatnot and everything was pretty much copacetic.
His neurologist began developing a new procedure a while back, and in need of test cases, he volunteered for an operation which would remove the damaged parts and hopefully ameliorate or eliminate the seizures all together. Everything went well, and his recovery was astounding, for about 3 years.
Then about 6 months ago my phone rang. It was a friend of his in a panic who had grabbed his phone and called the last person he had dialed, which was me. His reason for panic was because my bud had just fallen to the floor and was completely unresponsive and having difficulty breathing. I instructed him to roll him on his side and make sure he had a clear airway, then to hang up and call 911, which he did. I relayed all of the pertinent information to his dad, then broke down.
Turns out that for some strange reason, my bud had a pretty severe stroke, possibly related to scar tissue or some other complication of the procedure. I didn't know that at the time, but knowing his history and seeing such a remarkable recovery come crashing down was devastating. The thought that I was going to loose one of my best friends brought me to tears. My wife did a good job of trying to console my while I blubbered on her shoulder for a good 10 minutes or so.
He's been doing pretty well since then, but is still periodically a little off kilter. Don't know if there will be a next one or a last one, so until then we just go fishing. Usually catching, too.