Over the years, I've had 2 periods of a few months where I took frequent hiccup-like breaths. They were sudden deep gasps for air, as if I'd been very startled. They weren't every few seconds like hiccups, but maybe several over a 10 minute period. Both times this stopped on its own, but my doc had no explanation for it. Of course, my doc knew very little about CFS, though thankfully enough to diagnose it.