Kellie Greenhalgh said it was “extremely busy” when she arrived at the shop for the annual event, where readers meet authors, access early copies of books, and attend panels and workshops.
But she said that while there were hundreds of attendees, there was no staff present to give directions or assistance.
“I did not see a single member of Waterstones or event staff the whole time,” she told the BBC.
“The queues were all on the stairs, all in front of the lifts.”
The 33-year-old said she queued for an hour and a half to reach one stall: “I was shaking and did not feel well from the heat and stress”.
“One author had a panic attack and had to leave,” she added.
Another attendee, who uses crutches, says she was left “standing shoulder to shoulder with hundreds of other people” trying to hand an author a book to sign, and that she was twice knocked over due to overcrowding.