I was also going to note that I have worked shifts that are hard on sleep. When working an overnight shift, for example, I found it impossible to sleep more ht

I was also going to note that I have worked shifts that are hard on sleep. When working an overnight shift, for example, I found it impossible to sleep more htan 4 hours per day (day because you get to sleep maybe 8am). The funny thing is the impairment isn't linear throughout the day. There are times when it is really bad (1-3am) and times when it is pretty good (dawn, during the daylight hours etc). In general the only times I found myself impaired was at work. I have talked to people who worked in other industry overnight and their experience was the same. As far as I can tell, without tremendous amounts of caffeine, the brain seems to go partway to sleep, able to recover from approx. half of the outstanding sleep debt per day. Part of the problem is the way in which we use caffeine to compensate.