A 22-year-old female reports recurrent episodes of feeling detached from her body, as if she is "watching herself from outside." She describes the world as feeling "unreal, like a dream" during these episodes. She remains aware that these experiences are not real. The episodes last minutes to hours and have occurred several times per week for the past year. She denies substance use, trauma history, and has no psychotic symptoms. What is the MOST likely diagnosis?