It still marks a big improvement for Aston Martin, who finished seventh behind Alfa Romeo in last year’s championship.
“This is Formula 1, this is not a charity event, we have to have the pressure and deliver," Alonso said.
“Fifth in the Constructors' hurts a little bit because I think we were better than that, and we were hoping to be better than that at the beginning of the year.”
“In the Drivers', finishing fourth is a little bit unreal, fighting with the guys that we were,” he added.
“In fact, if you are fifth in the Constructors', normally you should be ninth and 10th in the Drivers', so it is a dream season for everyone in Aston Martin, including myself.
“It is completely unexpected, completely unreal to be fourth in the championship.
“As I said [earlier in the weekend], 2012 and this season for me are the best in my career and I was in a position that I could never have imagined at the beginning of the year or with the car performance we had.”