Odd

I've noticed this wierd thing when I get bad colds: at first, as my symptoms are just developing, I feel a bit ill and really miserable; then, when I'm fully unwell I feel physically much worse but get this sudden flush of feeling actually rather cheerful. Yesterday my cold was just starting and I was really very down; today I'm much more obviously unwell and I'm in an unusually good mood. Previously I've always assumed the grumpiness is because of how annoying it is to know you're coming down with something, and I've attributed the cheerfulness to the effect of people being nice to you once it's obvious you're ill, but I wonder whether there's more to it than that. Though it seems odd that a disease should make you happy. I suppose recreational drugs are mild poisons, so maybe it's like that.