Wow, sorry for the delay in responding. I didn't expect so many repiles from the community.
I sent a PM to PM (heh) and they responded that I had indeed used that amount of data. I actually lied when I said it was "seconds" later - it was actually seven minutes later.
My phone tracker still shows nothing close to that amount of data being used in that amount of time, but PM is taking the position that I did, so I don't really have much option other than to take their word for it at this point. I ended up purchasing a data add-on.
What I *suspect* happened, given that I was tethering at the time, was that Windows may have tried to download an update or something like that (I haven't got a notification on my PC to that effect, but I'll look into it). I had set the hotspot as a metered connection on Windows originally, but I landed up changing the ESSID of the access point, so Windows no longer had it set as a metered connection.
In any event, I *still* don't know why my phone isn't showing a spike in data usage. Generally my phone breaks down how much data is being used per app or service, including tethering services. Anyway I guess this will just be a mystery. I think my theory about Windows downloading its millionth update in like a week, as per usual, is probably pretty likely. I *hate* how newer versions of Windows just silently download updates without telling me, but that's another story for another day.
