A 30-year-old female veteran with PTSD has been started on prazosin 1 mg at bedtime for trauma-related nightmares. After 3 nights, she reports mild improvement in nightmare frequency but still awakens 2-3 times per night. She notes some dizziness when getting up quickly at night but her standing blood pressure in clinic is 108/68 mmHg. Which of the following is the most appropriate next step?