because you have either fouled a spark plug or lost a plug wire or maybe collasped a lifter, and also maybe burned a valve . there are more than a few possibilities.
If your check engine light is blinking that means an engine cylinder misfire has been detected . You can drive it in for repair , just avoid any rapid aceleration or deceleration because you can damage the catalytic converter
No, the check engine light does not come on because your gas is half way full. The check engine light will come on if there is a problem with the engine.
no a burnt out headlight will not cause a check engine light but if you go to most of the part places they will check the check engine light for free
There is a problem with the SRS...have a dealer check it.
There are pages and pages of things that can cause a check engine light. You need to have it checked with a scantool. Then the code can be diagnosed and repaired.