1.
If someone is in hysterics or is having hysterics, they are in a state of uncontrolled excitement, anger, or panic. (INFORMAL)
I'm sick of your having hysterics, okay?...
N-PLURAL: oft in N
2.
If someone is in hysterics or is having hysterics, they are in a state of violent and disturbed emotion that is usually a result of shock.
It was such a shock I had hysterics...
= hysteria
N-PLURAL: oft in N
3.
You can say that someone is in hysterics or is having hysterics when they are laughing loudly in an uncontrolled way. (INFORMAL)
He'd often have us all in absolute hysterics.
N-PLURAL: oft in N