2001 Ford Focus Car Suddenly Loses Power Cruising Along Set Speed Engine Still

The car suddenly loses power as I am cruising along at a set speed. The engine is still running fine, but I feel there is a loss of power to the wheels or a loss of forward motion and the transmission light comes on. After a few seconds, the power comes back and the light goes off. There is no sound nor does the car jerk. This has happened a few times in the past few weeks. I have checked the transmission fluid and it is fine. What is the problem? Thank you.