It’s three a.m., but you don’t need to check your phone to know that. You know it’s that time because you always wake up at three a.m. It’s like your brain is equipped with a silent, malfunctioning alarm clock that rings you awake each night despite your earnest intention to sleep soundly for a full eight hours. The funny thing is that everyone wakes up multiple times each night. But in most cases, these middle-of-the-night arousals are so brief and shallow that the brain doesn’t recall them in the morning.
