The victim identified as Karlee Daubeney in her 20s sand found herself helpless wrote ‘help me' messages in ketchup on pieces of cardboard in a desperate attempt to be let out, reported The Independent.
But her attempt to get attention of CCTV operators resulted into vein as they could not notice her. It wasn't until 7.30am the next day, when staff arrived to open the store, that she was freed.
The incident took place when was putting milk away in the walk-in chiller when the door shut behind her and locked her inside.
She tweeted after the incident: "Got locked in a f*****g fridge over night for 8 hours and work don't ask me if I'm okay, they ask if I can work tonight P**S TAKE".
"At first I was in a state of panic and I was looking for anything that could have opened the door," said Daubeney
"I was trying to write ‘help' on pieces of cardboard to slide under the door. I think it was with ketchup or mayonnaise.
"It got to the stage I was so cold I didn't have the energy to bang on the door and I only had leggings and a Subway top on.
"My muscles became so cold I found it really hard to walk for a few days, I had migraines and dry skin around my nose. When I went to hospital the next day I was told I was close to having hypothermia and I made myself as warm as I could when I got home."
She claimed to have suffered long-term effects from the ordeal, which took place last December.
She said: "I didn't leave the house for a long time afterwards as I was suffering from really bad panic attacks - it has been nearly a year and I still suffer from anxiety.
The franchise responsible for the store, CM Ventures, was appeared before magistrates on Monday. They have been charged with health and safety offences, to which they pleaded not guilty at a preliminary hearing at Cheltenham Magistrates' Court on 26 October.
A Subway spokesman said: "As this case is currently under investigation we are unable to comment further at this stage."