The teaching profession has always been challenging, while for various reasons the magnitude of observed stress in teachers has been continually growing over time. This study was conducted to demonstrate the relevance of stress in this professional group and to generate evidence for the benefit of primary school teachers and, indirectly, their pupils. To this end, we examined a large number of school teachers in a descriptive cross-sectional study. The survey comprised 786 primary school instructors aged 21 to 65 years, 646 women (82.2%) and 140 males (17.8%), and was performed from March to October 2022. Participants were asked about their gender, age, marital status, place of domicile, satisfaction with their income, whether their income met their needs, number of children, whether they cared for a person with a disability, work experience, alcohol use, eating patterns, and their height and weight for computation of their Body Mass Index (BMI). The survey included the Teacher Subjective Well-being Questionnaire (TSWQ), the Perceived Stress Scale (PSS), the Healthy Lifestyle and Personal Control Questionnaire (HLPCQ), and the Pittsburgh Sleep Quality Index (PSQI). The results showed that there were significant differences between the two sexes in age, marital status, work experience, smoking, alcohol use, and eating breakfast. Furthermore, there were significant differences between the two sexes in BMI, PSS Total, Dietary Health Choice, Harm Avoidance and Total HLPCQ. The variance of PSS Total was predicted by Sex, Teacher Efficacy, Total PSQI, Dietary Health Choice, organized physical exercise, social support and mental control, and Total HLPCQ. Between teacher efficacy, school connectedness, teacher well-being, organized physical exercise, social support and mental control, Total HLPCQ and PSS Total, the correlation coefficients were negative and significant at the <0.05 level. Between Total PSQI and PSS Total, the correlation coefficient was positive and significant at the <0.05 level. Between teacher efficacy, school connectedness and teacher well-being, organized physical exercise, social support and mental control, Total HLPCQ and Total PSQI, the correlation coefficients were negative and significant at the <0.05 level. In summary, we demonstrated that Greek primary school teachers experience significant stress, which is intertwined with their way of life, and reflected in significant decreases in their sense of well-being, quality of sleep, and overall life satisfaction, as well as in their standards of teaching.