There is actually a malady called "Altitude Sickness" from the effects of being up that high! Makes you very sleepy and yes, headaches etc. We experienced that several times going up to the Rockies and crossing the Continental Divide at Trail Ridge Road - 14,000 Ft altitude.

VOYAGER:
MC to FLL 11/07
MC/Dover 6/06
MARINER:
BCN / Ven 10/11
Alaska 2001|2006
Panama Canal 2003
NAV
Caribbean 11/06
Bermuda|New Eng/Canada 6/04
PG 5/05
OCEANIA
Nautica |Ist/Athens 6/07
Regatta|Baltics 6/08
Riviera 2013 Crossing -Istanbul to Miami