DD (8) is usually a happy, easy kid. But periodically (2-3 times per week) when she gets hungry or over-tired, she loses all perspective and emotional regulation. She can't stop a stream of terrible thoughts, catastrophises over whatever catches her mind, and gets into a complete sobbing state. We try to give her reasons why it won't happen, and calming techniques like deep breathes and thinking of nice things, but she either says it might happen or latches onto the next terrible thing. The only way to stop it is to get her food/sleep.
I expect this in a toddler, but is this normal for an eight year old?!
Examples are: saying that evil doctors will experiment on her and give her a popping out red and blue eye (she has vision problems, and had a symptom recur which triggered this) and not wanting to eat lunch because 'we might have poisoned it because we hate her' after a very mild, calm rebuke over not sorting something. I don't think it's really about any specific worries though: I think she just latches onto something to explain how she's feeling.
School report comments say she is calm, works hard, a bit reserved. At home, she's lovely, generally happy, often very funny, mood is more up and down than most kids - but not usually a problem except when she gets in these states. And then it's like a hurricane hits!
Is this normal? What can we do to help her (and us!)?