Stress is a word used to describe several physiological reactions to a person's environment. It is rooted in the "flight or fight" response in all animals which results in an increase in adrenaline, a faster heart rate, an increase in blood pressure, faster respiration and a heightened sense of awareness. It is also interchangeably used to describe the factors that will bring on such reactions, which vary from person to person.
Doctors often use stress as a diagnostic tool, for example, placing a patient on a tilt table to see if their heart rate becomes irregular, or putting a patient on a treadmill to increase their heart rate and respiration to determine their reaction.
Although stress is a normal reaction, too much stress puts strain on the organs, leaving a person susceptible to several forms of heart disease and even the possibility of stroke. Tranquilizers used to be a common treatment for persons who suffered from high levels of anxiety, but their use has generally been phased out due to the possibility of the drugs either being addictive or habit forming. Doctors today are more likely to suggest lifestyle changes.