Remember that sea-sickness is a real threat, even to the most experienced. If you are in a relay team, almost everything mentioned above will apply to your swim, except the fact that you will be spending one hour in the water, followed by 5 hours in the boat - the 5 hours on the boat can be a problem if you are sea-sick
Motion sickness is the nausea, disorientation and fatigue that can be induced by head motion. The first sign is usually an unhealthy pale appearance. Yawning, restlessness and a cold sweat forming on the upper lip or forehead often follow. As symptoms build, an upset stomach, fatigue or drowsiness may occur. The final stages are characterized by nausea and vomiting.
Horses, cows, monkeys, chimpanzees, birds and sheep have been reported in scientific publications to show motion sickness. Rats, unfortunately I suppose, do not vomit so cannot serve as experimental subjects.
According to research, nearly 100% of (human) occupants of life rafts will vomit in rough seas. 60% of student aircrew members suffer from air sickness at some time during their training. For vertical motion (heave), oscillation at a frequency of about 0.2 hz is the most provocative. Motion at 1 Hz is less than 1/10th as provocative. About 7% of seagoing passengers report vomiting during a journey (Lawther and Griffin, 1988).
Women are more sensitive to motion than men, by a ratio of about 5:3 . Women are more sensitive to motion around the times of their menstrual cycle This may be due to interactions between migraine and motion sickness