You are not working out, you are not dieting, but you are still losing weight quickly? Although it's not something that many people are concerned with and it may be welcomed by some people, unexplained weight loss is indeed worrisome. If you are experiencing weight loss for no apparent reason, then it may be a sign of an underlying health condition. The most common symptom of unexplained weight loss is dramatic or sudden weight loss, which is usually 5% of the weight of your body . It could have occurred over a few weeks or months. Other symptoms may include an inability to perform daily tasks, loss of energy, weakness, night sweats, pain, fever, loss of appetite and fatigue.