Mrs Falkingham had been drinking at The Vinci wine bar in Liverpool last Friday. Police said she left the premises with Mr and Mrs Keith who found her dead in their vehicle 12 hours later.
An employee at The Vinci said Mrs Falkingham was with a group of four friends who had drunk a "couple of bottles of wine" between 4pm and 7.30pm, when her manner changed suddenly.
"She went from being OK to suddenly being in a near-comatose state," he told The Daily Telegraph. "I've worked in these situations a long time and have seen plenty of people get drunk but I have never in all my life seen someone turn as quickly as that.
"She said she was starting to feel sleepy and then she just went. Her head went right back, I've never seen anything like it. I tried to speak to her to see if she was OK but she couldn't speak.
"I called the police and they told me to phone an ambulance, but before I had the chance, some friends of hers turned up and took her away."
A neighbour of Mr and Mrs Keith said he had not seen the couple since Friday.
"Kevin and Cathy are lovely people with three smashing daughters," he said. "No one is sure what has happened here. I woke up to find all these police cars swarming around, I've never seen so many."
A Merseyside Police spokesman said: "Officers were called to Eastwood, Aigburth, just after 10am by the owners of a Black Vauxhall Insignia car, who had found Nicole dead in the rear.
"Soon after arriving at the location, officers also discovered a cannabis factory with about 100 plants at the address."