Ya good call.
My first ever trans tasman flight was on a Qantas 747 out of Auckland to Brisbane.
The morning of the flight, I woke up with blocked ears, nothing unusual, my ears tend to wax up fairly heavily, and i often wake up with blocked ears.
Off to the doctors for a syringe out, being a saturday had to see the doc first, normally just goto the nurse. he had a look, ooohed and ahhhed and sent me off for a flush, said come back before i left.
Had the flush the and the nurse ahd a look and sent my on my way to the airport.
Got on the plane, was keen as, being my first international flight, thought cattle class service was awesome, could (can) only dream of what the first class was (would be) like.
An hour into the flight, things started going bad, and only got worse, my ears wouldn't pop with the pressure changes, it got so bad i thought my head was going to implode, spent the last too hours of the flight with head in my hands, and my eyes watering like i had stuck my head in a bucket of onions.
Was even worse on the decent, was bad enough I had thoughts in my head of hijacking the plane, just to stay in the air

We landed and headed for the gold coast, most of the way there i still couldn't get my ears to pop, and had a hard time hearing and my throat was sore as by now.
Off to the docs again, he took one look and ex pleated and asked if i had flown with my ears like this, i said yes and he said i was lucky to have ear drums left.
Turns out i had a tropical ear infection, and my ear canals had inflamed to the point where my canals where completely closed off, and there was no way a doctor should have let me fly with it, kinda wondered if the nurse knew that and why she bundled my out the door with seeing the first doctor a second time.
No wonder it hurt like hell and i couldn't hear anything, spent my first 7 days overseas anywhere on some various serious penecillin, just so i could fly home.
So good call, would hate to think what is would like with a head cold.