The PMHNP is evaluating a new patient, a 31-year-old woman who was referred by her primary care provider (PCP). She complains of feeling fatigued for the past 3 months, and this fatigue has caused her to stop socializing. Upon further questioning, she reports feeling uncomfortable sensations in her legs in the evenings. She describes the sensations as burning and tingling, and states that she has to walk around to get any relief. Which diagnosis best fits her clinical picture?