Don't fly with a cold or sinus infection

'One final related note: you often hear that you should not fly if you have a cold or sinus trouble. This is good advice, and you should take it whenever possible.

If the Eustachian tube is blocked (common with a cold), you can wind up with a bubble of high pressure air trapped in your ear. Ouch.

A co-worker was recently on a flight where the eardrum of the guy sitting next to him burst in flight, projecting blood and pus through the canal, suddenly cranking up the discomfort and damage caused by his ear infection. The flight attendant indicated that this happened more often than you might like to believe.'

Straight Dope