Anxiety is a diffuse, unpleasant, vague feeling of apprehension, usually accompanied by autonomic symptoms. It involves awareness of physiologic sensations such as palpitations and sweating, along with a subjective feeling of nervousness or fear. Unlike fear, which is a response to an identifiable present danger, anxiety is directed toward an anticipated or impending danger.

Reference: Kaplan and Sadock's Synopsis of Psychiatry, section “Anxiety Disorders,” states that anxiety is “a diffuse, unpleasant, vague sense of apprehension, usually accompanied by autonomic symptoms,” and distinguishes it from fear because it concerns impending rather than overt danger. Kaplan and Sadock's Synopsis of Psychiatry, 12th ed., Anxiety Disorders, p. 478.