Anxiety
 

According to Webster:

Main Entry: anx·i·ety
Pronunciation: a[ng]-'zI-&-tE
Function: noun
Inflected Form(s): plural -eties
Etymology: Latin anxietas, from anxius
Date: circa 1525
1 a : painful or apprehensive uneasiness of mind usually over an impending or anticipated ill b : fearful concern or interest c : a cause of anxiety
2 : an abnormal and overwhelming sense of apprehension and fear often marked by physiological signs (as sweating, tension, and increased pulse), by doubt concerning the reality and nature of the threat, and by self-doubt about one's capacity to cope with

Also see "Fight or Flight Syndrome"