不注意to be absent-minded

• 稍一失神，就会出事故。

  The slightest moment of absent-mindedness could cause an accident.

精神萎靡；精神不正常to be in low spirits; to be mentally ill

• 两眼失神。

  Both eyes are dull.

• 她显然有些失神的样子。

  She is quite obviously out of sorts.

【医】loss of vitality