The apprehensive anticipation of future danger or misfortune accompanied by a feeling of worry, distress, and/or somatic symptoms of tension.
Anxiety may be associated with symptoms of depression, poor concentration, insomnia, irritability, panic attacks, sweating, tremor, and nausea.

Fear is the emotional response to real or perceived imminent threat, whereas anxiety is anticipation of future threat (the focus may be internal or external).
These two states overlap, but they also differ, with fear more often associated with surges of autonomic arousal necessary for fight or flight, thoughts of immediate danger, and escape behaviors, and anxiety more often associated with muscle tension and vigilance in preparation for future danger and cautious or avoidant behaviors.

Adapted from American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. Fifth edition. Washington, DC. American Psychiatric Association. 2013. Internet. Accessed on May 23, 2016.