It's at this point in an illness where I usually get a sensation that I call a "cold euphoria." Basically, despite the fact that I do not feel well, I feel great at the same time. It usually is the strongest when I am not taking any kind of medication, so I know that medical side-effects are not the cause; however, I will not rule out the idea that it is a symptom of exhaustion.
I have never quite been able to explain the sensations I experience in a cold euphoria. I feel tired, but the good kind of tired, like after having spent the day applying physical labor to a just cause. My mind feels unburdened in that hazy way it feels when coming out of a pleasant day dream. My body, though tired, notes changes in the air, both in temperature and tactile sensitivity. Basically, I feel like I have come through some sort of trial in triumph and my mind and body are looking forward to a well-deserved rest.
This euphoria can last a few hours or a few days. I never clearly remember when it starts or when it ends; I only notice it when I am in it. When in one, I want little more than to wear comfortable clothes and just lay back either sleeping, reading, or playing a low-stress video game.
When I explain this to most people, I get the impression that they have not experienced anything similar. I figure that they probably chalk it up to another one of my eccentricities. Still, I wish more people could experience this feeling (without the use of drugs, I should add).