Curtis Justin Mills was put in the cell when he showed up drunk for an annual sex offender interview at the Blood Tribe police station in May 2011.
When he later stood up to get a meal tray, the 48-year-old fell backwards and hit his head on a concrete floor.
Medical staff examined Mills and, although he vomited, they believed he was going through alcohol withdrawal and decided he didn't need to go to a hospital.
Workers checked on Mills throughout the night and he was found dead early the next morning.
The judge heading a fatality inquiry into the death says staff should monitor injured prisoners more frequently and conduct visual checks rather than watching them on video monitors.
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