I found this great description on wikipedia and found it very interesting. I am only posting an excerpt but I think you would enjoy the full page. The link will follow this excerpt.
The physiological correlations of limerence are heart palpitations, trembling, pallor, flushing, pupil dilation and general weakness. Awkwardness, stammering, shyness, and confusion predominate at the behavioral level. There is apprehension, nervousness, and anxiety due to terrible worry that any action may bring about disaster. Many of the commonly associated physiological reactions are the result of the limerent fear. Some people however may find that these effects come most strongly either immediately or some time after contact with the object of limerence, and this is accompanied with an acute feeling of ecstacy or despair, depending on the turn of events beforehand.
The super-sensitivity that is heightened by fear of rejection can get in the way of interpreting the limerent object’s body language and lead to inaction and wasted opportunities. Body signals may be emitted that confuse and interfere with attaining the limerent object.
A condition of sustained alertness, a heightening of awareness and an enormous fund of energy to deploy in pursuit of the limerent aim develop. The sensation of limerence is felt in the midpoint of the chest, or in some cases in the abdominal region.[citation needed] This can be interpreted as ecstasy at times of mutuality, but its presence is most noticeable during despair at times of rejection.
http://en.wikipedia.org/wiki/Limerence
Great question by the way and I enjoyed researching it. I guess it was something that I never really thought about but was very impressed by what I found.
Good luck and best wishes.