Previous research has produced conflicting findings on how sleep affects emotional memories, suggesting it can either strengthen or weaken their emotional intensity. Rather than having a uniform effect, sleep's influence may depend on factors that determine the most adaptive outcome. To explore this, we examined whether the future importance of an emotional experience shapes how sleep alters the emotional intensity of the associated memory. Emotional memories were induced using a novel evaluative learning paradigm featuring a short film clip depicting an acted version of the Trier Social Stress Test. Some of the actors playing the evaluative panel with a critical or neutral demeanour were then introduced as committee members during the participant's own presentation a week later, thereby assigning future relevance or future irrelevance to the formed memories. We recorded changes in emotional responses to memory cues subjectively (valence and arousal ratings) and objectively (skin conductance) after a 12-h period of either daytime wakefulness (N = 32) or containing nighttime sleep (N = 34) and again one week later. Learning was effective, as indicated by more negative feelings and subjective arousal (but not physiological measures) in response to memory cues of the aversive committee members. Regardless of sleep, arousal decreased over 12 h and one week for the future-irrelevant compared to the future-relevant negative memory cue. Valence ratings remained unchanged. These findings suggest that future relevance influences emotional memories independently of sleep. While the benefits of healthy sleep may be subtle, emotional memory processing might be more vulnerable to disruption from poor sleep quality.