First, "North American-based pilots flying eastbound at night towards Europe are at increased risk of fatigue-related performance" issues.

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Those planning on flying this holiday may experience short-term side effects from fatigue and increased cortisol levels, the report details.

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Balpa, which commissioned the report, is warning that problems with fatigue could get worse under European proposals that would see the maximum flying time for UK pilots going up from 900 hours in a 12-month period to 1, 000 hours.

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Although jets are pressurized so that the cabin environment resembles an altitude of around 8, 000 feet, some people report that flying (possibly from the changes in pressure and resulting decrease in oxygen concentration) causes symptoms such as headache, fatigue and nausea.

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