I've been using my Zeo for a long time.  Usually, I go into deep sleep within an hour of falling asleep, but rather than having more deep sleep during regular sleep cycles, I get very little after this first longer period.  I tend to have regular REM and Light Sleep that cycles throughout the night.

I did  the new SleepAge calculator that is available  on this site and it seems to be typical at my age (63) to get deep sleep early during the night, but next to none later.  My deep sleep averages about 45 minutes nightly and I know that deep sleep decreases as we age. I'm curious as to why normal sleep cycles do not include deep sleep  except during the first sleep cycle.  

Any others with similar experiences or insights into this phenomenon?