I dont do that very often any more. I would only take mass amounts of viagra to come down when I had been up several days in a row. And thats not the only thing I would have to do to come down and fall asleep. I would also have to eat a large meal, take a few shots of Diphenhydramine , fuck or jerk off a couple of times, then drink a few shots of vodka.
Sildenaphil, vardenefil, etc all lower your blood pressure, so that helps you crash.
Its one of the things I hate about the boner drugs. Even 20 mgs of Viagra makes me feel tired.