When a person takes something that doesn't belong to him without permission, he is stealing. The stolen object can be as small as a piece of candy or as big as a car. It can be taken from someone he knows or from a stranger. It can be taken from a store, which is called shoplifting, or from someone's home. But either way, it's stealing.
People can steal words and ideas, too.
For specific medical advice, diagnoses, and treatment, consult your doctor.