1. To misplace or mislay someone or something in some particular location. In this usage, a noun or pronoun is used between "lose" and "in." I lost my phone in the airport somewhere. My parents actually lost me in a supermarket when I was two.

2. To become so mentally involved in or preoccupied by something as to be oblivious to everything and everyone else around oneself. In this usage, a reflexive pronoun is used between "lose" and "in." I love losing myself in a good book. He had lost himself in the stunning scenery, so he hadn't heard what I said.