The impact of mental wellness on the work performance and wellbeing of workers has generated much academic and corporate debates. Most recently, due to some high-profile cases involving the performance and wellness of sports people, conversations around the impact of mental wellness on work performance have dominated public discourse, yet the nature and degree of this impact has not been sufficiently studied and analysed and many questions remain unanswered. Indeed, there has been a growing awareness of the centrality of the role of mental wellness in the productivity of workers, especially in the Oil and Gas industry. Thus, this research sought to investigate how rotational work, its impact on sleep and endurance, affect workers in the Oil and Gas industry, using as methodology a simple random sampling of workers from the Port Harcourt metropolis, in the oil-rich delta area of Nigeria. To obtain data, this research used questionnaires, telephone interviews and cohort discussion session. Questions posed during this research focused on sleep and its perceived effect on endurance. The questionnaires were administered to the workers from selected international Oil and Gas companies located in Port Harcourt. Findings revealed that both sleep and the circadian cycle were negatively affected and impacting the self-reported well-being and productivity of the workers. From the data collected, 27.5% and 66.2%, which represented a total of 93.7% of the respondents, agreed and strongly agreed that their sleep was affected. 100% of the participants in the cohort session agreed that their sleep was affected. Furthermore, the interview sessions revealed specific details as more than 50% of the interview respondents indicated that the sleep distortion affected them even up to the first week of their time off. 48.8% and 37.5% agreed and strongly agreed to the fact that rotational work had effect on their endurance on site. This represented a total of 86.2% of the participants whose endurance level was affected due to rotational work. Over 60% of the participants in the cohort session admitted to feeling of extreme tiredness towards the end of their rotation period and prior to departure from site. The participants unanimously submitted that shorter rotation would give room for adequate recuperation and make work more productive and enhance the sense of mental wellness for rotational Oil and Gas workers.