I went back for more.
Despite the unpleasantness last time, I felt the benefits were worth it. Also, I'd paid for it.
So I used Sensodyne every day since my last appointment and I took 2 aspirin before heading in.
This time, I made it through 2 full 15-minute sessions (and finished the movie I'd started the last visit). The zingers were not remotely as frequent as the last time during the treatment. Whether that is due to the deep cleaning, the Sensodyne, the aspirin or some combination, I have no idea. It didn't hurt that I had experience on my side and I knew that the zingers typically only lasted 3 or 4 seconds. I could count through them. I did, on several occasions towards the end of the second treatment. Thankfully, even the dental assistant recommended stopping, saying "Look how white they already are!"
And it's true. My teeth are noticeably whiter (enough so that I'll actually follow the directions and skip the coffee for close to 48 hours, which is a huge weekend sacrifice on my part).
After the aspirin wore off, I definitely have been experiencing intermittent zingers. Now, almost 12 hours later pain-med free (I didn't take any more after the initial dose, perhaps this was an error?), I can say that two sessions definitely cause more residual nerve pain than just one.
Even so. I like my white smile. I'm pleased. And most importantly, I'm dead-set on avoiding the dentist at all costs for at least 6 months, and likely more, because I'm a procrastinator like that.