Lovesickness describes the informal syndrome of rejected or unrequited love and covers physical as well as mental symptoms. It is not to be confused with the condition of being lovestruck. Almost all humans suffer from love sickness one or more times in their lives. Although typically harmless it can lead for some personalities to serious physical or mental illness, suicide or possibly even death. In psychology, love sickness is seldom acknowledged.
When a person is "love sick," they can't think of anything but the object of their desire. Being love sick generally happens to younger people who have little or no experience with an actual consensual loving relationship. Immaturity paired with hormones and strong emotions may be the cause of love sickness. Poetry, songs and Shakespearian plays are full of the heady expression of love sick people, pining for the ones they love.
Despite its intensity, love sickness is a passing state of mind, lasting anywhere from a few days, to a few months. It's difficult to retain the intense level of emotion that love sickness awakens in the body, often the feelings lead the afflicted to either express his/her feelings or as time passes, the feelings lose their power as the reality of getting to know the real person takes away from the fantasy.