I couldn’t sleep last Sunday night. I had no caffeine during the day, and generally everything felt fine when I went to bed at 11PM, the remnants of a thunderstorm rumbling further in the distance as the cool air streamed through my bedroom windows. Post-thunderstorm cool nights are my favorite sleeping weather, and I drifted off to sleep comfortably. But I woke up at 3AM, feeling hot and stuffy and distinctly uncomfortable. The air wasn’t moving at all anymore, so I put on the fan and went back to sleep. Only…I couldn’t fall back asleep. I had no idea why.