I tend to follow some kind of a line of continuity in what I say when I'm talking, but it can branch off pretty randomly into related matters, rather than just stopping when I've made the original comment. And I also have a tendency to keep adding further explanations and clarifying analogies to what I've said, rather than simply asking the listener whether they understood my point. It seems to take some energy for me to keep a conversation reciprocal, to keep it switching fairly rapidly back and forth between me and the other person, and it's probably harder for me to do that when I'm tired, and even when I'm not tired I rarely achieve it. But I rarely switch to anything completely unrelated and random, however tired I am. Sometimes I'll notice something that fires up my enthusiasm and I might suddenly interject it, which probably would come over as random, but that's more an excitement thing than a tiredness thing. And these days it's probably under better control than it used to be.