Fear of sleep is proposed to contribute to pathogenic processes underlying trauma-related sleep disturbances. The Fear of Sleep Inventory (FOSI) and its short form (FOSI-SF) appear to be suitable instruments to investigate this construct, yet only English versions are currently available.

To facilitate the cross-cultural investigation of fear of sleep, this study aimed at providing a German version of the FOSI-SF, and investigating its psychometric properties as well as its associations with clinically significant PTSD and insomnia.

The German version of the FOSI-SF was generated following the principle of forward-backward translation and administered to a large online sample from the German general population (n=754), next to measures of PTSD symptom severity, insomnia severity, and sleep quality.

The German FOSI-SF has good internal consistency (Cronbach's α=.87). The factorial structure remains inconclusive because exploratory and confirmatory factor analysis detected Heywood cases. Convergent validity was confirmed by moderate to high correlations with PTSD symptoms, insomnia severity, and sleep quality (rs=.30 to .47). Participants reporting clinically relevant PTSD symptoms expressed significantly higher fear of sleep than participants without PTSD (ω²=.053). Furthermore, participants with insomnia reported significantly increased levels of fear of sleep relative to participants without insomnia (ω²=.011).

These results indicate that the German FOSI-SF is sensitive to the theoretically-related disorders of PTSD and insomnia. Overall, the German FOSI-SF offers an economic and practicable brief measure of sleep fears that can enhance further insights into trauma-related sleep disturbances.