Malaise - What is going on?

I don't know what the heck I drank last night, but I am so paying for it today. And really - I didn't even drink a lot (no, really). All day, I've been feeling like I'm operating on half of my usual brain cells and its so wierd. People talk and I know I should understand but I don't get it until way later. I had this feeling in Panama once as I walked across the border to Costa Rica (it was something about suddenly feeling like a refugee) and I thought I had malaria. It really freaked me out. It freaks me out today too because everything just feels so crazy...