1. Unexplained weight loss

Losing weight without trying might sound like a dream come true, but in reality it can signal a health problem. If you don't have a body mass index of 30 or higher (obesity) and you've lost more than 10 pounds (4.5 kilograms), or more than 5 percent of your body weight, during the past six to 12 months consult your doctor.

An unexplained drop in weight could be caused by various conditions — including overactive thyroid (hyperthyroidism), diabetes, depression, liver disease, cancer or disorders that interfere with how your body absorbs nutrients (malabsorption disorders).