http://englishgrammarsecrets.com
HAVE KITTENS means to be worried or anxious.
It is mainly British English and informal.
American English has the expression HAVE A COW with the same meaning.
When he heard his daughter had bought a motorbike, he had kittens.
I had kittens when I heard she was going on a TV reality show.
She had kittens when her husband went for the job interview.