na-adjective
hysterical; hysteric
Describes a state of extreme emotional agitation, often with loss of self-control. Used as a na-adjective.
彼女はヒステリックに泣き叫んだ。
She cried out hysterically.
ヒステリックな反応は避けたい。
I want to avoid a hysterical reaction.
ヒステリー is a noun meaning 'hysteria' (the condition), while ヒステリック is a na-adjective describing hysterical behavior or state.
Loanword from English 'hysteric', ultimately from Greek 'hystera' (womb), reflecting historical medical beliefs.