It seems that my stubborn, macho attempt to "work through" my sickness was quite stupid. The liver (an organ I'd never given any thought to at all) is where we get our "bursts" of energy. Exerting myself physically apparently puts a lot of strain on my liver, which makes me feel really dreadful.
The good thing is that I managed to get the strain of hepatitis that leaves no permanent damage behind.
The bad thing is that there's no treatment. I just have to refrain from physical activity, and hope the nausea goes away soon.
Don't you love the stuff you find on Flickr? The artist gave me permission to use this image.