Originally Posted by jojiobi
Why is it that the recommended pattern is 90 minutes then 4.5 hours?
Think of it as 1 sleep cycle, and 3 sleep cycles (with the average being around 90 minutes). It's recommended largely because it seems to work much better than other combinations.
Sleep cycle length will vary from person to person, and change slightly over time (my own cycle is gradually shrinking). How long are your cycles currently? NB
: if you're not sure how to measure your cycle length, just keep track of the times you naturally wake up following the nap. This'll give you a pretty good idea.