Having an erection for that long is bad for your pen1s. Viagra increases blood flow to pen1s and the valves of the veins that take the deoxygenated blood back get extremely overloaded, if these valves get damaged you may no longer be able to hold an erection without viagra. The reason for this when you are erect the valves partially close to keep the blood in pen1s, when you have too much blood flowing and too little going back, the veins and valves get too overworked.