I had to 'floor-board' the accelerator to get out of someone's way on the interstate. After I took my foot off the accelerator, the engine continued to rev over 5000/rpm for a few seconds. The car slowed down (so it did not continue speeding up) but it continued making noise and revving.

I was on the interstate so I probably was going 70mph. The RPM slowly went down to normal after a few seconds. Nothing else seemed to be wrong. Temperature normal, no shaking, etc.

Any ideas?

That sounds like possible transmission slippage or poor gear/ lockup clutch engagement, you should get that looked at. If it is the case, best thing to probably do would be have the transmission fluid serviced, they'll have to drop the pan. If there's a lot of metal in the oil, there's problems.

It could also be normal too. The car tries to adapt to your driving and may have been trying to hold on to a lower gear. If I suddenly floor my car it and then come off the accelerator it will stay down a gear or two ready to deliver another sudden burst of power.

Some people try to tap the accelerator to get the car downshifted before passing on highways.

Either way don't skimp on the transmission service.

Question is, how long was it stuck revving? Sounds like it was just in lower gear lol I've found sport mode sometimes hold the gears slightly longer.