How many deaths in each of the last five years have been caused by drugs prescribed for insomnia or other sleep-related conditions.

The National Records of Scotland report Drug Related Deaths in Scotland in 2018 was published on 16 July 2019. It states there were a total of 1,187 drug related deaths in 2018.
The report provides extensive information on the drugs implicated in or probable cause of death. Most drug-related deaths are people who took more than one substance. Of the 1,187 drug-related deaths in 2018, there were just 68 for which only one drug (and, perhaps alcohol) was found to be present in the body.
Specific analysis of drugs prescribed for insomnia or other sleep-related conditions is not included in the report. In addition the report does not link to prescribing data therefore it is not possible to determine if drugs were prescribed to the individual prior to death.
However, the report is accompanied by supplementary tables SUB1 and SUB2 which provide detailed information on drugs and other substances which were reported as being present in the body for drug-related. These tables include drugs which are known to be prescribed for insomnia.
The full report and supplementary tables can be found at the following link,https://www.nrscotland.gov.uk/statistics-and-data/statistics/statistics-by-theme/vital-events/deaths/drug-related-deaths-in-scotland/2018