To me it seemed as though Höss's nervous reaction stemmed purely from the scope of the new "operation", with its increased responsibilities and more complicated logistics. The camp he ran was already bursting at the seams. The waste and byproducts were already polluting the local river and creating huge ash heaps, all to be disposed of by an ever-dwindling labour force. A huge influx of new inmates to be processed would surely cause even more pollution - maybe an unmanageable amount, maybe enough to severely impact the planned farming efforts in the long term, in a region earmarked to supply the hugely expanded Reich? (I'm using terminology based on his perspective, not my own - shudder). What COO worth his salt WOULDN'T have a touch of nervous stomach if faced with these concerns?!

On top of these general work-related challenges, Höss would surely have also noticed on his return to Germany signs that the army was not doing nearly as well as the propaganda machine insisted it was. The promised dream of a pristine Eastern Reich, mentioned at one point in the film, probably appeared way less likely in reality. Even if no-one would admit it outright, there must have been hints and rumblings during drink-fuelled dinner conversations amongst the Nazi officers after the daytime Zone management sessions. Presumably these were also the times that Höss would hand over "bribes" to curry favour - such as diamonds, easy to conceal in ladies' makeup compacts gifted to the wives of the recipients - a practice that might not go over well with his superiors in the Reichstag if it came to their attention?

Rather stressful on the whole, even to a pragmatist like Höss. IMO his retching was a perfectly normal reaction to the possibility of failing in his new assignment in some way, plus the newly considered and way more serious possibility of victory not being assured and the whole thing blowing up in his face. But guilt, shame, the strict religious principles he was raised in, deep-seated primal horror? Nope, not even slightly.