When thinking about someone or something, one would feel a strong emotional fluctuation in their heart. This emotion would make one feel uncomfortable and painful. That's because emotional fluctuations cause the brain to release chemicals like endorphins and Dopamine, which can make people feel pain and pleasure, and that's why we feel sad or excited. When we miss someone or focus on something, our brain will constantly search and recall these emotions, which will cause our brain to be highly active. In addition, these emotions can also make us feel nervous and uneasy, which can lead to pain. When we miss someone or focus on something, the best way is to try to divert our attention to do something we like. This can help us relieve pain and discomfort.