The PMHNP is evaluating a new patient, a 33-year-old woman. She reports feeling "keyed up" most of the time, having constant muscle tension, and excessively worrying about "every little thing." These symptoms have been occurring for about 9 months, and they are causing her significant distress at home and at work. She takes no medications, and her lab work and physical exam are negative for an underlying medical cause for these symptoms. What diagnosis is most likely?