Temperature gauge and engine speed

I have began to experience an odd issue wiht my 2005 Nissan Frontier SE. While driving down the road at normal operating temperature, the hand on the temp gauge will "fall out" all the way down to the C on the gauge, like when you turn the ignition off, and the engine idle will start revving between 2000 and 3200 rpms. The temp hand willthen pop back up to the normal level and the engine idle will return to normal. It may happen once or it may happen over and over several times.

Has anyone ever had this happen or know the direction to point me in getting this situation solved?