Stress is a dynamic psycho-physiological response to any given demand that we perceive as outweighing our capabilities. Some stress is quite helpful and even improves our performance. However, too much stress often causes negative symptoms, many of which are quite severe if stress persists. Stress negatively affects relationships, work, our mental health, and our physical health, as well. We all experience stress from time to time, however, when feeling overwhelmed, chronically tired or lethargic, or experiencing persistent somatic symptoms (e.g. tight chest, muscle tension), it's time to manage that stress instead of feeling managed by it.
Stress management is a skill - it doesn't happen by accident, and it takes time to learn how to recognize symptoms, understand their origin, and craft a productive plan to both proactively and reactively mitigate it's negative effects.
"Five Things You Should Know About Stress." National Institute of Mental Health.