Post-dive fatigue is very common. An explanation I was once given that makes sense to me is that a diver will have microbubbles remaining in the tissues after a dive, even when staying well within the no-decompression limits. The more dives in a short period, the more nitrogen is loaded, and the more microbubbles may be present. Off-gassing all this nitrogen taxes the system in some way, causing fatigue. This explanation supports the reports of divers that diving with nitrox reduces post-dive fatigue.
We may throw around heavy terminology like "sub-clinical DCI" pretty freely when we consider fatigue, and in fact, studies have shown definitively that there are microbubbles present even in divers who practice slow ascents, make deep stops, and generally dive conservatively. With that information, it seems likely that all of us have some greater or lesser degree of "sub-clinical DCI" after every dive.