English Idioms and Phrases: Having Kittens
If you're 'having kittens' or someone is going to 'have kittens' it means that the person is experiencing extreme nervousness, excitement or panic / worry about something. It is usually used in a negative way.
"Where have you been? Your mother has been having kittens!" (very worried)
There are many idioms and phrases in the English language that relate to cats (kittens being baby or young cats) and this one has a medieval origin.
In the middle ages there was a great fear of women being witches - and that they would put a spell or a curse on people. Cats were linked with witches as it was believed that witches owned one. This is where many superstitions about cats originate.
When a woman was pregnant and in a lot of pain it was rumored that a witch had placed a curse on the woman and that she was now pregnant with cats, or that she had cats in her stomach and that they were scratching her to rip out of her. Therefore they would say she was having kittens or giving birth to kittens. This means the original phrase was more about pain, but over time it became worry.
Alternatives / Synonyms
To be worried - to worry.