Lyme Disease
Lyme disease—a bacterial infection that causes everything from muscle and joint pain to fatigue, all from a tick bite—is usually initially identified by a rash, but that isn’t always the case. Because some people don’t show the go-to symptom, a 2005 study from the National Institutes of Health found it takes an average of 1.2 years for a patient to be accurately diagnosed with the disease, and throughout that time they’re dealing with all the symptoms.