Scary thing happened this morning-sign of major transmission problems or just a fluke?

Driving down the road this morning seemed like the was stuck in gear. i took my foot off the gas and the speed kept increasing, i had to brake to slow down & it sped up again without touching a foot to the gas pedal. pulled over, put it in park & it was running at over 2000 rpms while parked. turned it off & started it up & it started at over 2000 rmps again like it was in drive. restarted it a second time & ran fine afterwards...major problem or was it because it was the coldest morning this year?