Check engine light comes on, but won't stay on

I have a 2006 Chevy Colorado 4X4 with 118,000 miles. About 1.5-2 months ago my check engine light came on for a coupe of days. When I finally found a local repair shop that could be trusted to take it to, the light went off and the repair shop told me to wait until if comes on again before I bring it in because it is easier to tell what is wrong if the light was on. I drove it for about 2-3 weeks and nothing. Then one night it came one and went off again by the next afternoon. It did that again a few more weeks later (3 times total of coming on and shutting off before I can get it in). It runs the same, but should I worry?