@Rod: You're right, at this point it is just correlation; as I said, "anecdotal". However, the actual duration of the symptoms seemed to be shorter, as well as less severe towards the end of the effective period.
As I said, anecdotal, and completely subjective besides, but over the last year, Viagra's effects on me have been pretty consistent, i.e. pop the pill, 30-60 minutes later pop the nut, and 1-2 hours after that get the stuffy nose and minor headache, which lasts until the 4-6 hour mark after taking the pill, along with some residual stuffiness the next morning.
Contrast that with the completely unscientific observation of a shorter total duration, i.e. 3-4 hours, along with no trace of the stuffiness in the morning, when I get a second shot 30-60 minutes after the first.
Of course, my observations in no way take into account my general level of well-being on the days when multiples happened. It's entirely possible that I was better rested or something, which enabled both the second shot and fighting off the symptoms faster. However, if others were to report the same, it would at least be a valid basis for a hypothesis, though it would need much testing to verify.