It’s natural for your weight to fluctuate during the year. Maybe you eat a bit too much during the holidays and gain a bit of weight, or you come down with the stomach flu and end up dropping a kilo or two-a slight swing on the scale is normal and nothing to worry about.

But if you drop at least 5 percent of your body weight in less than six months-and you can’t pinpoint a good explanation for that weight loss-it’s time to let your doctor know what’s up, says endocrinologist Dr Anne Cappola. That means if you’re 68kg, a weight fluctuation of about 3-4kgs in a short amount of time should be a red flag.“It’s not common to lose a significant amount of weight without an obvious reason,” Dr Cappola says. “If you’re losing weight and nothing’s changed with your diet or activity, you need to worry about that a little bit.”

In fact, unexplained weight loss could be an early sign of a serious health condition, says internal medicine expert Dr Kerry Hildreth. Here, eight health issues that could explain why you’re losing weight so suddenly.