SHAFAQNA (Shia International News Association) -- The 73-year-old woman felt faint at the store in Roubaix and went to the toilet. But when she came out later she found the shop deserted and locked up.
French media say she set off the alarm repeatedly and spent the night wandering the aisles, but nobody came.
A member of staff found her safe but exhausted on Tuesday morning.
The local newspaper La Voix du Nord says the woman was taken to hospital for a health check. She had tried unsuccessfully to get some sleep in the Intermarche supermarket's staff office, and had not helped herself to any new year treats from the shelves.
Roubaix is near Lille and the Belgian border.