【Precipitate】 ,  【headlong】 ,  【abrupt】 ,  【impetuous】 ,  【hasty】 ,  【sudden】  as applied to persons or their acts or behavior denote characterized by excessive haste and unexpectedness.

【Precipitate】 especially stresses lack of due deliberation; sometimes it suggests prematureness and is therefore especially applicable to decisions or to actions based on decisions.

【Headlong】 throws the emphasis on rashness and lack of forethought; it is used to describe not only persons and their acts but the qualities exhibited by such persons or in such acts.

【Abrupt】 when applied to actions suggests complete lack of warning or, sometimes, unceremoniousness and when applied to manners or words, it usually implies curtness.

【Impetuous】 implies violence or vehemence; as applied to persons, it often also suggests impulsiveness or, at times, extreme impatience.

【Hasty】 stresses quickness of response and often suggests thoughtlessness and hot temper rather than impulsiveness.

【Sudden】  is distinguishable from  【sudden】 meaning unexpected only by its added implications of extreme hastiness or impetuosity.