Tailored Treatment of Insomnia in Social and Health Care Sector Shift Workers in Occupational Health Care

The goal of this clinical trial is to evaluate the usefulness of cognitive behavioural therapy for insomnia (CBT-I) tailored to shift workers in the social and health care sector. The study will also learn about the shift workers' experiences of the acceptability and feasibility of CBT-I and investigate which features of shift work and individual characteristics promote or interfere with the effectiveness of the tailored CBT-I. The main question the study aims to answer is: • Does CBT-I tailored to shift workers in the social and health care sector improve perceived insomnia severity, insomnia symptoms, mental health and quality of life? Researchers will compare CBT-I to a control intervention (short sleep hygiene counselling) to see if CBT-I works to treat insomnia in shift workers. Participants will: * Participate in the research intervention (CBT-I tailored to the shift work context; six individual sessions) or the control intervention (sleep hygiene counselling; one individual session) * Complete the measures (sleep diary, actigraphy and questionnaires) at baseline, after the end of treatment (12 weeks after the first session) and at 6 months after the end of treatment.