It all started with a tweet. An American tourist, David Willis, found himself locked in a London Waterstones bookshop which had closed while he was still browsing. After attempting to open the door and setting the alarm off, then taking several phone calls from the security guards and police to no avail, he took to social media. “Hi Waterstones, I’ve been locked inside of your Trafalgar Square bookstore for two hours now. Please let me out,” the Texan tweeted. It worked: he was freed soon after.

At the time Willis did not realise what a stir his tweet had caused – but the next morning he was interviewed on Good Morning America and ITV’s Good Morning Britain. “I did it because I was frustrated and bored, and mostly I was just hoping to get a response from Waterstones,” Willis said last week from Paris, where he was continuing his holiday.

Waterstones decided to make the most of its embarrassment this weekend – branch manager Matt Atkins said they were “mortified” by what had happened – and the fact that hundreds of tweeters had declared Willis’s situation to be a dream, with one saying: “I would kill to be locked up in a bookstore.”

On Friday, an organised sleepover was held in its Piccadilly store in partnership with travel website Airbnb, with 19 guests chosen through a competition in which they had to say which book they would like to read on the night (their choices varied from Franz Kafka to Roald Dahl to Cormac McCarthy). The 11 men and eight women were a mix of ages and occupations, but all were excited about the idea of a nocturnal literary lockdown.

“There’s something really exciting about being in a bookshop when it’s dark and there’s no one else there, and it’s a bit out of bounds; like you’re an explorer and you’ve broken into a library,” said Clare Elcombe Webber, who took her mother along.

Her plan, like that of many others, was to browse, read and eventually get some sleep. “I want to look at vegan cookbooks as, for some reason, I never find any good ones,” said Nick, a medical student (we would later find out that he found some to his liking). His friend Guy, a politics, philosophy and economics student at Oxford University, was looking forward to finding a quiet little corner and getting immersed in a book. All they had been told was to bring pyjamas – two of the guests showed up wearing them. After a tour of the building, which is Europe’s biggest bookshop, they were interrupted by a Poirot lookalike and a Jeeves impersonator, who both read fragments of books for the guests.

Afterwards, sleep expert Richard Wiseman gave a talk about tips to combat sleep deprivation and insomnia. The guests were glad to hear that reading before bed was not a bad habit (as opposed to looking at any kind of screen). However, Wiseman said that what you read does matter: “It influences your sleep and dreams, so it’s best not to read anything too stimulating.”

He conducted an experiment, dividing the guests into two groups, giving them either a romantic novel or a horror book, and asking them to read an excerpt before sleeping and to write down their dreams. “It worked,” said Elcombe Webber, who was given the romantic read. “I had a very fruity dream, with all my friends having sex in an art installation and me telling them off.” She had also been looking at art books earlier in the night. “I blame him entirely.”

Then came the stellar moment of the night, at least in terms of visible excitement: the unveiling of the sleeping area. Staged in the children’s section, there were gasps of pleasure at the sight of carefully placed air mattresses, bookish goody bags and unicorn slippers.

After all this activity the lights were dimmed. It was time to do what they all came here for. Books were read, chess was played, tweets were sent and quiet conversations had until the early hours. Nick and Guy read short stories by Oscar Wilde and Mark Twain to each other. A comic-book lover, Deepali, read a fragment of Art Spiegelman’s Maus and found a strange humour book about penguins.

“At one point, I popped up and scared this girl who was doing the Christmas window. When I realised I wasn’t registering what she was saying, I thought it was time to go to bed,” said Jimmy Tomlinson, who works in fashion e-commerce.

All the guests said they had managed to fall asleep at some point. Half read more than 25 pages, but none read an entire book. Tomlinson and his friend, Damiano, spent the night walking around barefoot. “The best part was the freedom. It’s rare to be allowed to do something like this in a public space in London,” he said. Tomlinson compared the experience to some scenes in Stanley Kubrick’s film The Shining – but only in the sense of being a group of people locked in a large, otherwise empty building. “At 3.30am, we said to each other, ‘can you imagine if we could always live like this?’”