Chris,
It is the same with dd6. When she is getting sick she is all out of sorts emotionally. And it is always after she's gotten sick that we think back and say "duh, we should have seen this one coming."
We also find that we have a drama queen when she is really bored with her life. By this I mean that she isn't being challenged at school, and we've not been doing any activities at home. Then anything can set her off, and it is usually at the strangest times.