Hung up on is a commonly used phrase which refers to being obsessed with something or someone. However, there are many synonyms that can be used to express the same idea. For instance, fixated, obsessed, preoccupied, captivated, absorbed, or engrossed can be used to replace hung up on in a sentence. Each of these synonyms highlights the strong emotional attachment or focus on a particular subject. Using alternative words not only enhances your vocabulary but also adds nuance to your writing. So, whether you are describing yourself or someone else's behavior, remember that there are many ways to express the idea of being hung up on something.