BOAC is correct. Its known as sinus barotrauma or barosinusitis. In your case the frontal sinus (air space in bone above your eye) was involved and yes it's bloody painful.
On descent trapped air in the sinus at low (cabin) pressure cannot equalise with ambient pressure. To fill the void swelling of the lining of the sinus (mucosa) occurs. This acute swelling +/- bleeding leads to pain.
Decongestants usually do the trick or don't fly if you have sinusitis/cold.
Full link here:
http://www.emedicine.com/ent/topic595.htm
All pilots need to be aware of this.