Hi Batsheva,
from my master's thesis at
http://members.shaw.ca/oldsite/My_Master%27s_thesis.htm

"The availability of tryptophan through
increased insulin production, in response to sugar ingestion, increases
uptake of competing large neutral amino acids  into muscle cells. This
increases the relative serum concentration of tryptophan, which is
resistant to insulin.  The relative increase in serum tryptophan, following
a rise in insulin,  leads to a competitive advantage to tryptophan,  for
transport across the BBB. Increased tryptophan has been shown to lead to
increased levels of serotonin in the brain "

The sense of euphoria that comes from eating something sweet is quite 
real. I don't know much about it, but apparently there is a similar 
dynamic at work in chocolate consumption.

Best Wishes,
Ron

-- 
PK