Thanks, everyone, for your support yesterday—your kindness brought me to tears. I just love and appreciate this community so, so much.
The info we have now is that FIL had an apparently minor heart attack (define "minor," right?); he went in early enough that they were able to take care of it before it became critical, thank goodness. He had to have a stint put in and, after that, was feeling a lot better.
He's still in atrial fibrillation and the plan is to see if the heart regulates itself by this morning. If not, they will defibrillate this morning. If that goes as planned, he'll probably stay tonight for observation and go home tomorrow.