Eating a roast beef and mustard sandwich is one of life's simple pleasures* - except for when the mustard flavour seems to go up your nose to create a horrible burning sensation! 

I get the same effect from horseradish too - but nothing else causes this when I eat - it is unique to those two condiments...and can be almost painful!

Can anyone explain what is happening here?

* apologies to vegetarians - cheese and mustard/horseradish instead?