gauge needle problem please help

The past 4 days on 2 occassions when just turning key to allow dash lights to display all my needles (fuel, rpm, speed, temp) went side to side for a couple minutes then reset to normal. i have a 2000 windstar. battery and alternator are about 2 1/2 years old. no dimming of lights when vent is put on high, has not died or needed a jump recently. any idea if anything else would cause this besides battery or altenator. probably started car and drove 12-15 times and only happened twice.

It is possible that the voltage supply to the instrument cluster is varying.
This could be a connection issue......wiggle & reseat connectors......or a issue with a voltage regulator on the instrument cluster.....
I would expect a connection issue first.......oxidation on a pin in a connector can do this....and a simple unplug & plug back in is often all that is needed to solve the issue.

There are also the ground terminal wires attached behind the front driver plastic, internal left hand side fender wall. The ground screws being loose have caused this issue also. You may want to clean them and check tightness.