Not a pleasant experience! Did you pump the brakes with the engine running before taking to the road? It should only require a few pump actions of the brake pedal to restore positive (normal) pressure, certainly not require 5 minutes of pumping. When last have you checked your brake fluid level?
BMW E90 330i (M) '05 (His) | (Hers) BMW E46 320i f/l (M) '03