Okay, you borrow money at 0% interest rate (that means that you will have to return the same amount you borrowed, you name it), which is essentially the same if you just had that money. Inflation as well as deflation is 5%, your profit margin is 2%, when will you suffer losses, and when will you earn profits?
The point is that the nominal interest rate is not the same when there is inflation and when there is deflation.
Nominal interest rates (those you have to pay) will be much higher in an inflationary situation than in a deflationary situation. That's the whole point.
In the 70-ies, when there was 2-digit inflation, you also had 2-digit interest rates on a savings account for instance.
The more there is inflation, the higher will be the interest rates. The more there is deflation, the lower will be the interest rates. So you can't say "let's keep the (nominal) interest rate constant - say 0% - and calculate the case of inflation and deflation".