Was it something I ate?
Massive insomnia. Was working on my paper for this week (I am SO far behind), but I didn't get far. It's one of those passages where I'm looking at it and I don't actually have much to add that doesn't seem obvious already. Anyways, switched away from that to working on the project I'm working on for work. Before you know it, it's 4am, and I still don't feel particularly tired.

On the other hand, I do have a 10am meeting, and I don't think I'll be particularly awake by that time, so I probably should try to sleep. We'll see how well that goes.