I hate the way "mood" is overloaded. I can be in a good mood when my MOOD is depressed. The boost in mood just has a short shelf life. But if I am sick and depressed, lifting spirits even temporarily is far less likely to happen. I also have a harder time holding up the facade of being okay so others can tell I am depressed (I manage to hide it much of the time).

When I am hypomanic, I can be switched from euphoric to irritable if I get really stressed. Getting sick is stressful, so it can make that switch.