What do you call someone who overreacts to everything?

What do you call someone who overreacts to everything? If you want only a single word instead of a phrase, then “volatile” (easily provoked, intentionally or accidentally, to strong emotions and behavior) and “hysterical” (tending to react in an extremely emotional way) approximate your intended meaning.

If you want only a single word instead of a phrase, then “volatile” (easily provoked, intentionally or accidentally, to strong emotions and behavior) and “hysterical” (tending to react in an extremely emotional way) approximate your intended meaning.
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