Strange hardware monitor readings

This morning I was playing Call of Duty 4 when the game minimized itself and I got a warning message, along the lines of "Your CPU fan isn't working properly, turn your system off and check it" or something.

I opened up CPUID hardware monitor, and watched as the TMPIN2 reading slowly increased from 36°C to around 40°C, then it spiked to just above 100°C for just a moment, going back down to 36-40°C.

This caused me a bit of panic so I turned off the system. I unseated and reseated the CPU heatsink, but turning on the hardware monitor again, TMPIN0, TMPIN1, and TMPIN2 all spiked up to above 100°C and back down before long.

Also, one of the fan readings (FANIN1), which normally runs at around 670 RPM, read 0 for a moment, and then went back to normal. A few seconds later it read 0 RPM again, and again went back to normal. This happened several times. As I type this out, however, the fan reading looks stable.

These temperature spikes, and the weird fan readings; should I be worried? The Temperatures under the name of my CPU didn't change at all (all cores maintaining about 36°C) so I don't exactly know what the TMPIN readings are for. But these spikes of temperature can't be a good thing?

My CPU is an AMD Phenom II x4 955 BE, not overclocked with stock cooling.