I'm glad to hear about your false alarm, and it confirms my own experience.
Prior to going on IVIG nearly two-and-a-half years ago, I would catch everybody's colds, flu and stomach viruses and each one of them would precipitate a potentially deadly episode of SCLS.
Ever since being blessed with IVIG, (a) I usually don't catch anybody's colds, flu or other ailments anymore -- which makes sense, because IVIG gives us extra immunities against all sorts of illnesses -- and (b) on the rare occasion that I've caught a cold, it has not triggered an episode of SCLS.
And I know this not only because I feel otherwise normal, but because I have monitored my blood (with a HemoCue device) and have confirmed that my hemoglobin concentration readings remain normal.