How do you respond to dark chocolate?
I think one of the simple answers is that chocolate contains endorphins and milk chocolate has a fairly-high sugar content unless it is very high quality.
Also, sugar is not something that the body has to digest--not like other foods anyway--and it is a very fast way for the body to obtain energy when digesting food would not be possible due to low energy and body resources. So basically, eating milk chocolate allows you to bypass the normal digestion process that takes a great deal of the body's energy (at least 80% on any given day).
Overall though, it weakens digestion if you eat enough of it, which is relative to every person, but it tends to build--like if you're eating it daily. So, you get more energy day to day and can regulate your blood sugar to a certain extent, but it inevitably ends in a crash because the already-weak digestion has been further compromised.