Symptoms preceding sids?

Unusual irritablity. There are no definite symptoms. Excessive irritability and "cold" (ur) symptoms have been reported but they are obviously non specific. The most important one is brief periods of apnea (no breathing) for about 10 seconds in sleep. The peak age is at 3 to 4 months so that would be more ominous at that age. Unfortunately there are often no symptoms at all.