The computer may, somehow feel nausea.
But if the claim is that this world is what you would expect a material world to be like and also claim that sensations are computations - then you must be able to demonstrate that some computation must produce the feeling of nausea.
I don't see why, when my claim is that my own thinking is the result of some computation as well. It is perfectly reasonable to say a calculation cannot necessarily derive itself. Didn't Godel demonstrate some such?
In fact, isn't it the case that, despite our best efforts, the details of the quantum realm cannot be calculated, even in principle (at some level)? If uncertainty is a feature of the material world, it cannot be decomposed entirely to binary, step-wise recipes.
However, all is not lost. We can do a kind of reductive anti-calculation. We can take something that does feel nausea and start removing parts to see if the nausea goes away. This, I believe has been done. So, while we may depend on a complex universe to create the feeling of nausea, we can degrade the machine doing the calculation in a manner that corrupts the sensation. And we do this by way of material removal from a biological system (as in blocking nerve impulses) - the "machine" doing the calculation.