When did insomnia become a problem (19th century?) and why?

Farming folk typically used to lead active, outdoor lives ...

And they were not drugged up on caffine ...

So they got a good night's sleep.

(Well that's my theory.)

As towns and cities were wbuilt poeple began to worry about there next
door neighbours
and the things they got down to

emlok

I expect that monotheistic religions with their strong sense of good
and evil and the promised consequences of the latter gave folks
sleepless nights.

A social problem? Considered to be a health problem? 

There is a biblical verse (Esther 6) where a king "cannot sleep" all
night. So people knew about insomnia back then. And I am sure that if
you'd read a medieval herbal (a book regarding the attributed
qualities of plants) you'd find there also references to insomnia (not
by name, see etymology here:
http://www.etymonline.com/index.php?term=insomnia).

It is possible though, that Victorian society, which had attempted to
control certain issues (especially sexuality), expressed special
interest in sleep (and lack of it), as a key to one's well being,
emotional and sexual desires, etc.

This book might be of interest to you:

At Day's Close: Night in Times Past 
http://www.amazon.com/gp/product/0393050890

In caveman days, stress was defined as people or animals in your midst
that would kill you if they had a chance. If this stress caused a
chemical reaction that led to fitful sleep, that would allow the
caveman to hear the predator and defend himself, thus saving his life
and allowing him to live to become our ancestors. Other cavemen
lacking this reaction led to an evolutionary dead end. Today we may
lack murderous predators but the stress of daily life still gives us
fitful sleep and robs us of good health.  So the answer, Teacherman,
goes back way before recorded history.  BigBlue

As far as I know, the earliest records of insomnia in ancient China,
but I do not know the specific age, insomnia was not in the 19th
century, the study of the reasons is because of psychological problems