The early stages of any new relationship are always the most intense. This is the time when the exhilaration of meeting the right person is the most pronounced, and we feel immediately close and may even become focused on thinking about them frequently or on an ongoing basis.
This is typically a period of time when all of our emotional energy is on the relationship. Hormonal changes in the body, including higher levels of adrenaline, create a high level of emotional awareness. The levels of serotonin, which naturally calm and relax a person, are low, leading to a heightened sense of every interaction with the person who is the object of your focus.