Does anyone know why I feel this way?

Sometimes I feel like I’m not entirely here. I go about life normally, I go to school, I eat food, I enjoy life, and sometimes I don’t. While I’m doing all this I feel like I’m not exactly here…in my body. Like everything is fuzzy and I can’t tell the difference between what is real and what’s not at times. Like I’m just in my head watching. I forget basic stuff sometimes on especially bad days. Like what I ate for lunch and even have to remind myself what day of the week it is.