According to these articles until sometime after 17th century man did not
sleep 8 hours straight through. Instead there were two four-hour sleeps
with an hour or two of awake time in between.

http://www.alternet.org/health/154424
http://www.bbc.co.uk/news/magazine-16964783


One of the references thinks the time in between might have been important
for stress management and relaxation.

Unrelated to this I have been doing a lot of research on natural vision
improvement all of which state that relaxation techniques are important. I
may be grasping at straws but I was wondering if the change in our sleep
pattern has had a negative effect on our vision.


Susan