I have the same experience. My threshold seems to be about 8 days - meaning that I can resume exercise more or less ok after slacking (or being ill) for 8 days,

I have the same experience. My threshold seems to be about 8 days - meaning that I can resume exercise more or less ok after slacking (or being ill) for 8 days, but after 10 days it costs a lot more and I feel worse afterwards. Of course it is more like a ramp than a binary thing, but there's a "step" around the 9th day in the graph.