I agree, it seems from what you say that
Reggie passed away of old age. Probably while sleeping as he was in his usual position. In the end, wouldn't we all choose to go that way if we could, peacefully and at home. There are always the 'what ifs' that dilligent owners go through ... but don't beat yourself up over the 'what ifs', because without any earlier symptoms, you could not have predicted what might happen and, even then, may not have prevented it.