Brad has been in a state of incessant worry for almost half a year now. he has trouble sleeping and breathing. dr. simons, a psychiatrist, asks brad detailed questions about his symptoms and medical history. brad tells dr. simons that he cannot stop worrying and is constantly nervous. brad also complains of muscular tension and stomach problems. after conducting a quick examination of brad’s symptoms, dr. simons discovers that brad’s incessant worry does not have a particular cause, and it has taken a physical toll on brad’s health. which of the following disorders is dr. simons most likely to diagnose brad with?