Michael Phelps has been experiencing a recurring nightmare two years out from the London Olympics.
The greatest swimmer the world has seen keeps dreaming that he is racing over 400 metres individual medley, one of the toughest events in swimming, but cannot complete the breaststroke leg.
Luckily for Phelps, his nightmare has never transpired in real life because, as his coach Bob Bowman puts it, that is "the event that defines him as a complete swimmer."
Phelps had thought about giving up the event after the 2008 Beijing Olympics where he won an unprecedented eight golds medals but it is back on his schedule and the training is gruelling.
No wonder the 25-year-old American is having sleepless nights though he should have no real reason for concern.
The 400 IM is one of four individual events Phelps will contest at this week's Pan Pacific Championships in California. He will also swim the 200 IM and both butterfly events, plus the likelihood of two relays.
He is not swimming freestyle this time but will still be expected to come away with a stack of medals, mostly gold. Even when he is not at his best, he remains the one to beat.
The Pan Pacs, to be held in the southern Los Angeles suburb of Irvine starting Wednesday, have attracted 336 competitors from 21 nations and could serve as an early guide to the 2012 Olympics with the likes of Phelps still experimenting with their schedules and a new crop of swimmers starting to emerge.
In the short term, they will be a contest between the United States, Australia, Canada, Brazil and Japan, with the Australia-US rivalry particularly intense, as dual Olympic gold medalist Natalie Coughlin has been explaining to her younger teammates.
Her first exposure to the extent of that competitiveness was at the the 1999 Pan-Pacs.
The event was held in Sydney, as a warm-up for the 2000 Olympics. Coughlin turned 17 on the second day of competition.
"I got to witness it first-hand," she said. "I still remember that last relay (the US and Australia were first or second in each of the team races). It was so loud, you could feel the sound waves in your chest. That was amazing, to be part of that."
While the focus will again be on Phelps, the attire and times of all the swimmers will be a hot topic.
This week's Pan Pacs will be the second major international event to be swum under new international rules banning the so-called "body suits" that the majority of swimmers were using in the last few years. The first event was the European championships which ended on Sunday in Budapest.
Designed to aid buoyancy and reduce water resistance, the polyurethane suits were deemed responsible for swimmers setting and re-setting world records, even those that were once considered untouchable.
Phelps lost his 200 freestyle world record to Germany's Paul Biedermann at last year's world championships in Rome but it was Biedermann's lowering of Ian Thorpe's 400 freestyle record that really convinced him the suits had to be scrapped.
"I really thought no one would ever break that record," said Phelps, who supports the current ban on suits.
"That was Thorpe in his prime. I thought that was one of the hardest records in the book."
"This brings the focus back to the sport of swimming, People will have to find out the hard way that you have to put a lot more hard work in, and you have to be in better shape."