Have a look at this and see if it helps you to understand: flip (your lid) - definition in British English Dictionary & Thesaurus - Cambridge Dictionary Online
Pushing her hair off her forehead, Mom said, “That’s Izzy. Not all Brannicks have the same abilities. I can’t sense the presence of Prodigium the way she can. Anyway, when I realized that I’d been living with the very thing I was supposed to be fighting, I—”
“Flipped all the heck out?” I supplied.
“Big time. And then I realized I was pregnant with you, and . . . well, you know the rest. All the moving, all the hiding.”
Flipped all the heck out??
Have a look at this and see if it helps you to understand: flip (your lid) - definition in British English Dictionary & Thesaurus - Cambridge Dictionary Online
Had a hissy fit.
Went a little crazy.
Freaked out.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
Lost the plot.
Context is important. Please provide enough for us to be able to deal effectively with your question.
Your thread title should include all or part of the word/phrase being discussed.
If you just want to know the meaning of a word, try OneLook Dictionary Search first.