Swimmer's trance 

(n.) A condition of daydreaming while swimming laps for competitive competition/practice. The tendency of someone to have such a condition while swimming generally reflects their vulnerability of daydreaming and can impair their memory such as not being able to recall how long of a distance they are swimming, what stroke they may be swimming and how long they may need to swim it for. This phenomenon generally occurs more frequently during a longer swim for swimmers at a swimming distance rate of x/y=1/1.5 where x, equal to one, is the average length of the swam distance per a workout or meet and where y, equal to 1.5, is the added distance in which a swimmer may have higher chances of being subject to swimmer's trance. Therefore, if the average distance swam by a swimmer was 200 meters during his/her workout or competition per each time he/she swam again in their workout then swimmer's trance would likely occur more frequently at distances of 300 meters or more. For this reason many long-distance events in a swim meet now have counters in which another person flips a sign with rotating board windows to indicate the number of laps already swum. Usually a solid red square or rectangle is used to indicate that upon reaching the next wall after this flip turn that they should stop swimming and almost eliminates the chances of swimmer's trance affecting a swimmer's time in competition.

Mike suffered from such a bad case of swimmer's trance that he couldn't lead off his lane for practice with concerns that he would forget what they were supposed to be swimming.

Swimmer's trance by Ohh Baracuda! February 15, 2007