Diseases are abnormal conditions that impair normal body functioning and can be caused by various factors like infections, disorders, or injuries. Some common diseases mentioned include cancer, autism, stroke, obesity, arthritis, flu, hepatitis, hernia, fibromyalgia, lupus, allergies, leukemia, gout, multiple sclerosis, hypertension, psoriasis, acid reflux, sleep apnea, meningitis, diabetes, anemia, asthma, restless leg syndrome, pneumonia, bronchitis, and heart attack. Symptoms of diseases can include pain, dysfunction, distress, or death.