Systemic inflammation is a condition in which the body's immune system is activated and causes inflammation throughout the body. It can present with a wide range of symptoms, including fever, fatigue, joint pain, and difficulty breathing. It can develop slowly over time, or it can occur suddenly and quickly. It can be caused by a variety of conditions, such as infections, autoimmune diseases, and certain medications. Systemic inflammation can manifest differently in different people, and the symptoms can range from mild to severe.