Good quality sleep is central to all areas of human health [1]. Sleep deprivation is associated with poorer cognitive functioning and a greater risk of suffering serious diseases including cardiovascular disease, obesity, diabetes, Alzheimer’s disease, and psychiatric [2], [3], [4], with an increase observed in recent years [1], [5].

Among emergencies, there are two large groups: hospital emergencies and out-of-hospital emergencies, which are those in which the medical team goes by ambulance to the site of the emergency. Both groups work in highly demanding situations [6], which can lead to greater job dissatisfaction and poorer sleep quality [7]. The working shifts of these professionals is usually structured in variable shifts in hospital emergency departments and 24-hour shifts in out-of-hospital emergencies, which may be a barrier to good sleep quality due to the alteration of circadian rhythms [1], [5], [8], [9]. Therefore, the working shift is associated with more occupational accidents, more metabolic, cardiovascular and mood disorders [1], [5], [9], [10], and stress [10], [11], and may contribute to poor work performance [5]. In addition, the problems derived from poor sleep quality can lead to increased daytime sleepiness.

Excessive daytime sleepiness is defined as the inability to stay awake and alert during the major waking episodes of the day, resulting in periods of irrepressible need for sleep or unintended lapses into drowsiness or sleep [12], and it is a problem that affects daily performance, having a great impact on people's physical and mental health [13]. The Spanish Sleep Society determines that it is a problem that affects approximately 5% of the population [1], while scientific studies show a prevalence ranging from 16% to 30%, depending on the type of work and the characteristics of the study subjects [14], [15], [16].

All these problems are also influenced by the person's level of optimism, as a beneficial relationship has been observed between optimism and sleep quality [17], [18], [19], [20].

Considering the above, it is important for emergency workers to have a good quality of sleep, to avoid errors in practice derived from lack of attention [5], [9], [21]. Therefore, our aim was to analyze the quality of sleep and sleepiness in hospital and out-of-hospital emergency departments, as well as the differences between the two services, and to study their association with sociodemographic and occupational variables.