If you overdose on something will there always be an adverse reaction?
Like any NSAID, it can cause problems if overused. It would take days to weeks and perhaps longer for the problem(s) to become evident. The most common one is GI upset including diarrhea. It can lead to ulcers among other GI issues. Google the medication and read the side effects.
Overdosing on steroids has increasing benefits, or the benefits tend to be proportional to the dose. Sides tend to happen over time instead.
Why do you wish to overdose on mefenamic acid for your discomfort. Just take a normal dose if the pain is really unbearable. It is better to avoid the medication all the same. Instead, improve your health by taking healthy foods and doing regular exercise. (Also, if you read and respond to that 'MessGe me anonymous' stuff, you'd probably go into rigors as well. Don't you know?)