Why do I feel good mentally when I'm sick?

Whenever I'm mildly sick with a slight fever or cold, I feel like I'm on cloud 9 mentally. It's like everything is clear. I know what I want to do, I'm not afraid of anything, I feel happy and I can find joy in even little things. It has happened so much that the thought of getting better the last time I fell ill made me little sad. Because I knew as I began to feel better the feeling would fade.

I've even thought if there were pills someone could take to give some mild symptoms of illness just so I could get that light feeling again.

I'm not sure, could it be hormonal? Is it that there's something my body releases when I'm sick that it doesn't when I am healthy?