"Become lost in" is a common phrase used to describe getting completely absorbed or immersed in a particular activity or thought. However, there are several synonyms that can be used in place of this phrase, such as "drowned in," "engrossed in," "absorbed in," "enveloped in," or "consumed by." Each of these words offers a slightly different shade of meaning, but all convey the sense of getting lost in something, whether it be a book, music, a daydream, or a particular task. Whatever the context may be, these synonyms allow for a more varied and nuanced way of expressing the idea of becoming completely lost in something.