Does the phrase "this person is having a cow" comes from the word conniption?
I just made the connection today, and realised I have no idea how to translate conniption in my own mother tongue.
I'd say "having a cow" is similar to the phrase "having kittens", more anxiety related, IMO.
Conniption is similar in meaning, but not quite the same ...It's a fit of rage/hysteria and is a common slang phrase in the southern US. A conniption fit requires hand and body gestures like throwing your arms in the air in FRUSTRATION and eye rolling. I think it's been around since the 1800s, so quite a bit longer than "having a cow".
ETA : it has been suggested that it is a corruption of the word canapshus or captious.