Answer:
Each person has different patterns in IED, so there is no definitive answer. Some people (myself included) will experience them in "clusters" have episodes of varying intensity once every few days for several weeks, and then returning to being completely normal for several more weeks or months after that. Others experience them evenly spaced, having one major episode every so many months. Many people who suffer from IED experience episodes sporadically, however, and may experience two episodes only a few days apart, only to go for several months or sometimes over a year without a single occurrence. These variations apply person to person, though, and if you observe the individual, you can eventually figure out their individual patterns.