I just recently had a bad case of this. It usually only happens when on cycle, and gets particularly bad when I go through periods of physical and mental stress.
The last few months have been an emotional roller coaster ride for me, I am one month into a decent cycle, and I physically ran myself into the ground last week. This case was the worst I have had it, but it has improved greatly over the last couple days since I rested/slept almost all weekend.
My diet has been unusually high in sugar lately, which I hear can contribute to it as well.