The timing and location of the Oxford Street "terror" scare created a "perfect storm" for people to panic, a leading psychologist has told Sky News.
Dr Glenn Wilson also said shoppers who took to social media to describe the "more dramatic side of things" did so to boost their own self-esteem.
Hundreds of people fled Oxford Circus Tube station on Friday just after 4.30pm, prompting numerous 999 calls to police reporting shots had been fired in the station and on Oxford Street.
Shoppers, many screaming, were told to take cover in buildings on Europe's busiest shopping street as armed police stormed the area over fears of a terror attack.
Dr Wilson, who has published studies on human fear conditioning, said: "It was a perfect storm really: the prime time for shopping, a rather commercial kind of event, lots of tourists about.
"So, the anxiety about a terrorist attack would have been extremely high at that point.
"It just takes a minor incident to spark it off.
"An announcement that there's been an incident and people should make their way out – they begin to yell and scream.
"And of course the vulnerable people get trampled over when you get panic."
Various rumours quickly spread via social media, with some saying shots had been fired, while others said there had been a gang fight on the platform at Oxford Circus station.
There were rumours that a bomb had gone off and some even said they had seen people who had been shot.
An hour and a half after the first 999 call police stood down their response after firearms officers found nothing.
Dr Wilson said people take to social media in situations like Friday's to "impress their friends" and reduce their own anxiety.
He said: "Social media always looks for the more dramatic side of things, people like to impress their friends about how they're in the centre of events, it's good for their own self-esteem.
"They also use social media as a way of reducing their own anxiety. Connecting with other people is a natural human urge when you're in absolute difficulty."
Several people were hurt and nine were taken to hospital, including one with leg injuries, after panic erupted in the packed station.
British Transport Police (BTP) said they believe the incident started after an altercation erupted between two men on the platform at Oxford Circus station.
They released pictures of two men they wanted to speak to over the mass evacuation and later tweeted that a 21-year-old and 40-year-old had both attended a police station voluntarily and had been interviewed.
A BTP statement said: "We understand that incidents like this cause panic and concern.
"We would therefore like to thank Londoners for their patience during this incident. Our officers will remain highly visible on duty this evening to reassure the public."