So I was driving at what I thought was around 50 when I look at the speedo and see it say around 20 and around 1500 rpm. This seemed real doubtful, especially since I was in 6th gear. When I came to a stop at the next traffic light I watched the needle go to zero, below zero and even more below if it could.

After I restarted the engine at a gas station everything seemed back to normal but I wonder if this is the start of a (no doubt expensive) sensor of some sorts taking a crap.