A roughness in the throat is usually the first thing I notice. Unchecked, it develops into a cough, sore throat, sneezing, and at the peak a couple of days of being completely unable to function.

This happened about once a year on average before I discovered I could banish them by willpower, since when it's been more like once in five years, generally from extreme circumstances like being caught in the rain on a bike ride without adequate clothing.