What does it mean when you have an 'check engine light come on and stay on for a few days then goes off?

I have a 97 mercury villager and it had went to the shop for new belts and readjusting the radiator clamp. It was fine til a few days later when the engine check light suddenly started coming on and staying on... the car shut down once and then i recranked it and it started driving slower... later on that same day the engine light stopped coming on and it went back to driving normal and i had no more problems since- what gives- is my problem over or should i still be concerned?