The really important bit is not to sleep too long. A lot of people think the longer you sleep the better. With controlled rest this is a dangerous assumption. It is extremely important that the nap be no longer than forty minutes. Sleep inertia may (I emphasize may) also have played a role in the Air India Express disaster. I have done a great deal of night flying over recent years and my experience is that a few minutes napping can be extremely helpful, but it needs to be carefully monitored.