Scoobs,
As a Doc and a pilot I can tell you it is almost certainly one of your frontal sinuses giving you grief.
These connect to your nasal cavity through a wee tube that blocks off from time to time.
If you happen to be descending then the pain from the expanding air trapped inside can really grab your attention - it has done mine once or twice.
I would recommend you leave it well alone unless it is a perpetual problem, it is possible to cranialise the sinus (nasty op - last resort) but I would live with it unless it is always troubling you.
SB