The test to see if you are fit is easy. On the ground, pinch nose, shut mouth and blow. Both ears should 'pop' at more or less the same time, as your eardrums are forced outwards. When you swallow a few times they should go back to feeling normal as they clear.
If they don't you're not fit to fly.
The risk is the pain caused by a sticking ear can be intense and distracting and the physical damage, permanent.