How to prevent headaches after air travel<br>Try ibuprofen. Oftentimes, headaches that occur during or after flight are due to a sudden change in altitude. The painkiller ibuprofen may effectively prevent altitude related headaches before they begin.
Headaches that occur during or after flight are usually due to a sudden change in altitude.
The text says "Oftentimes, headaches that occur during or after flight are due to a sudden change in altitude." Often is not [necessarily] the same as usually, but the model thinks it is.