Temperature gauge goes wacky?

What's up everybody? I have a 99 Galant (4 Cyl). I was driving this morning for about 20 miles at 70 -75mph. All of a sudden I see my temperature gauge jumping up beyond the red and settled at the highest point it could go. I pulled over, looked under the hood but didn't see any type of smoke. I turned the car off and the needle went all the way down. As soon as I turned it back on the needle jumped up again. I waited about 20 minutes and continued on my way for another 45 miles at highway speeds. Has this happened to anyone? Could it be the fan? It wasn't running when I pulled over. Could it just be some wackiness w/ the gauge? It dropped to the halfway point once when I had to brake, but went right back up when I hit the gas.
Any insight is greatly appreciated!!!