A reader asks:

 Dr. Terman, I have read with great interest the summaries of your research, and some of your blog postings. I am wondering if you have ever come across patients whose sleep time and wake time are incredibly reliable, who don’t have a mood disorder, but who have an abnormally low afternoon dip? I have long had this problem — no issues with falling asleep, staying asleep, or waking up, but a dip after lunch that is so severe that I find myself walking across the street with my eyes closed. I am as perky as can be in the morning, but it is the most uncomfortable fight to try to stay awake in the afternoon. Nothing I have ever tried, other than an actual prescription stimulant, has had any effect, and I don’t like how I feel on the stimulant. I recently traveled to Israel, where I thought I’d be incredibly jet lagged, but, surprisingly, I felt far better than at home in the DC area. The only things I could think of were that it was so incredibly blindingly bright all day long every day, or that the time of my afternoon dip would literally have been while I was asleep because of the time change, and that my rhythms didn’t adjust in the week that I was there. I purchased a light box on the advice of my doctor, but I can’t find any information on how I should use it. I’m wondering if you’ve ever met anyone like me? It would be the greatest gift if I could have my afternoons, and not have to plan my days around needing a nap. Doctors have long told me that it’s healthy to take a nap, but it’s one thing to decide to take one, and it’s another to absolutely require one.


You had the correct insight. The afternoon slump can occur with or without depression. If you measure the interval between the slump and the midpoint of nighttime sleep, they’re about 12 hours apart. (This is separate from the “post-prandial” slump some people experience after a heavy midday meal). You don’t need to spend all day in “blinding bright light” to counteract the slump. The principle is to get to the light box as soon as you sense the onset of the slump, and not wait until it gets severe. This can nip the slump in the bud, even with 10,000 lux light exposure as short as 10 minutes. Some people will need longer, so you’ll need to experiment. There are days when the slump comes a bit earlier or later, so don’t set the light session by the clock. Rather, be attentive to the onset of the slump. This technique works for many people, but not for everyone. If it fails, and you have control of your work space, raising ambient light level in the afternoon to about 2000 lux – from ceiling or desk fixtures – including the light box – is another approach. Don’t overdo it, however, or you may experience jitteriness, headache, eyestrain, or sudden mood shifts that interfere with work.