There’s not a globally agreed upon definition of back on the horse. Well perhaps among the horsey set, but not in my circles. You could get back on it just once. But the expression implies more than that and sets up an expectation of things to come. Weekly things to come. I imagine friends, “friends” and strangers eagerly scanning the net and facebook pages over toast and coffee, or other delicious items they have photographed and shared, wondering what the hell I did over the last week and when they might expect to know.