In a very emotional way, often with extreme laughter, crying, or loss of control.
From Greek 'hystera' meaning uterus, as ancient doctors wrongly believed emotional outbursts came from the female uterus. The '-ical' and '-ly' suffixes were added later.
The word 'hysterical' is based on the ancient Greek idea that women's emotions were caused by their uterus—a completely wrong medical theory that got baked into our language and is still used today!
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