Last night I slept extremely well. I slept about eight hours and woke up feeling really good. In the past I’ve slept this well only after being on my feet nine or ten hours. Yesterday I was on my feet maybe four hours. I usually sleep well but this was a distinct improvement.
What caused it? Yesterday had many unusual features (like most days), but I did deliberately vary one thing:
1. I looked at faces (actually, my face in a mirror) earlier than usual. Usually I start around 7:40 am; yesterday I started about 7:10 am. (Background: I discovered that seeing faces in the morning improves my mood the next day. For example, seeing faces Monday morning improves my mood on Tuesday. And makes my mood worse Monday night. Details here.) I’ve done this before — watched the faces earlier than usual — and hadn’t noticed anything unusual. Yesterday may have been different, however, because three days ago I changed something. I always listen to something (audiobook, a Google Talk, This American Life episode, etc.) while I look at my face in the mirror. Three days ago I moved the sound source directly behind the mirror.
This is my best guess why my sleep was better than usual. But yesterday was unusual in several other ways as well:
2. I went outside (in the shade) 30 minutes earlier than usual.
3. Usually wear contact lenses while sleeping but didn’t.
4. Usually wear a tooth guard while sleeping but didn’t.
5. Salmon for dinner, which isn’t unusual, but I had more than usual.
6. No aerobic exercise.
7. Did a lot of chores I’d put off. (Peace of mind?)
8. On the preceding days, the sound source was behind the mirror. In other words, it was the cumulative effect that produced better sleep.
9. The end of a cold.
Now I’ll do all sorts of things to test these possibilities.
There’s a saying No one believes a theory but the theorist; everyone believes an experiment but the experimenter. This illustrates why. The experimenter can see all sorts of confoundings and special circumstances that others cannot.