The effects of abstinence from digital services and/or devices (aka “digital detox”) on mental health have received increased interest in recent years. Regular breaks and abstinent periods are advised to help individuals who overuse digital technology, but the psychological benefits and related consequences require empirical attention. While some studies have examined the impact of abstinence from smartphone or social networks (SN) on mental health, there is a dearth of literature on the effects of abstinence from Instant Messaging (IM) services. This study examined the association between a 72-h abstinence from IM and subjective craving toward IM, IM withdrawal-like symptoms, affect (positive and negative), and time spent on IM. Thirty-five undergraduates who regularly engaged in IM were assessed one day before (baseline), during (daily), one day after, and one week after refraining from using IM for 72 h. Results revealed a moderate-to-large decrease in craving (η2 = 0.438) and negative affect (η2 = 0.386) during and after the abstinence, whereas withdrawal-like symptoms and positive affect remained stable (η2 between 0.009 and 0.140). One week after abstinence, participants reported a small-to-moderate decrease in their IM use (d = 0.32). These results suggest that abstinence from IM is associated with reduced preoccupation and/or obsession (i.e., craving) with this use and lower negative affect. However, withdrawal-like symptoms and positive affect did not change. These findings support recommendations that IM users experiencing negative affect states may benefit from short-term abstinence. Further research should investigate strategies to support users in undertaking abstinence and regulating their digital device use.