Hello, the check engine light is triggered by the engine control module when it see a malfunction with the input or out put senors of the engine management system or emissions. depending on the fault the engine will probably run good, and the module has to be scan to pull the fault codes( Dtc's) to point the area of trouble and then diagnosed.
The dealer is an option but they will charge you lots for diagnostics. See if you can find a trusted repair shop close by. As far as serious if the engine is running ok now then it
can't be serious. But it should be diagnosed it may eventually effect the way the engine runs or fuel economy.