“How many times a night do you wake up?” he asked. I’m up three or four times a night (usually to pee), but I almost always fall right back to sleep. He nodded gravely. “That’s really not good, all those interruptions. Sleep quality is just as important as sleep quantity.” The interruptions were undermining the amount of “deep,” or “slow wave,” sleep I was getting, something above and beyond the REM sleep I had always thought was the measure of a good night’s shut-eye. But it seems that deep sleep is just as important to our health, and the amount we get tends to decline with age.
