I recently filled up my tank in Costco and started driving. I felt that the horse power of my car has gone down a lot. I drove it for a day and my check engine light came on.
I googled the issue and there were suggestions to tighten the fuel tank cap, which I did last night. As of this morning, the check engine light is still on and the horsepower of the car still feels lower than what it used to be.

Today I tried driving on a motorway and the car struggled to reach 70. With the accelerator fully pressed, it still can't go any faster. From time to time it keeps getting bursts of power. Also I noticed that cruise control doesn't work anymore.

Is this something to worry about or will go away by itself?