In Dr. William Dement’s book The Promise of Sleep, he writes about the Multiple Sleep Latency Test (MSLT) a measure of how much sleep debt a person has. The MSLT measure how fast it takes you to fall asleep (from less than a minute to greater than twenty minutes). The faster you fall asleep, the more sleep debt you have.
While in the general case, it does make sense. But it seems to me that it would not apply in all cases.
For normal sleepers, it makes sense that if you are awake longer and have acquired greater sleep debt, you would be more tired and sleep and would fall asleep quicker. Take the case when a normal sleeper got a full night’s sleep and wakes up naturally, his/her sleep debt is like zero. If you were tell the person to go back to sleep, it would probably take quite a while.
However, there are chronic insomniacs where their sleep debt is great (having sub-optimal sleep for a night or two), but are still unable to fall asleep easily (certainly taking more than 20 minutes). So how can the MSLT be an accurate measure of sleep debt in those cases?