Stress is the physical and mental condition that results from an individual's response to real or perceived circumstances in their environment. This response may vary greatly from one person to another, due to upbringing, physical condition, environmental influences, and conscious as well as involuntary habits. Therefore, factors that produce negative stress in one person may actually motivate another positively. In most cases, mild stress can actually foster productivity and problem solving. However, continuous levels of overwhelming stress can result in harmful physical and behavioral problems. For this reason, it can be helpful to be familiar with symptoms of serious stress, so that the sources can be identified and managed in a healthy manner. Stress can produce feelings of continuous anxiety, fear, irritation, moodiness, low self-esteem, failure, and embarrassment. Further, it may stimulate obsessive thoughts, preoccupation with tasks, or absentmindedness. Sometimes, heavy stress can lead to non-characteristic behaviors such as stuttering or other speech difficulties, irrational crying bouts, impulsive actions, nervous laughter, teeth grinding, exaggerated clumsiness, overeating, or self-starvation. Certain personalities may respond to stress by an increase in drug, alcohol, or cigarette use. Physically, the body may react to ongoing or critical periods of stress with excess perspiration, faster heartbeat, trembling, nervous ticks, dry throat and mouth, constant fatigue, frequent urination, or sleeping difficulties. It's also fairly common for gastrointestinal problems to result such as diarrhea, indigestion, nausea, and vomiting. If any combination of these symptoms is observed, it may be helpful to take time to uncover the sources of stress. A few common causes of stress include: beginning or ending a job, starting or leaving school, moving, getting married, having a baby, getting divorced, changing a long-standing aspect of one's lifestyle, and losing a loved one. Less specific, ongoing causes may include deadlines, competition, financial difficulties, constant noise, and significant disappointments. It's often possible to learn coping skills to manage stress positively, once the symptoms and sources are understood.