Stress is simply a reaction to a stimulus that disturbs our physical or mental equilibrium. In other words, it's an omnipresent part of life. A stressful event can trigger the “fight-or-flight” response, causing hormones such as adrenaline and cortisol to surge through the body.
Memory makes us. If we couldn't recall the who, what, where, and when of our everyday lives, we would never be able to manage. We mull over ideas in the present with our short-term (or working) memory, while we store past events and learned meanings in our long-term (episodic or semantic) memory.