Sometimes I feel weird, like I feel like I am somewhere else?? Why?

Sometimes I feel like I’m not really in a certain place or feel like a different situation is happening. People have suggested depersonalization, but from what I have heard, none of it matches up with what I feel. Sometimes I will zone out and forget where I am, it will feel like I am walking in a memory. Its hard to explain honestly, but it causes me to forget obvious things, things I should know. A couple times I have walked into school and didn’t know where to go even though I have been there for more than a year and always went to classes. I forgot what rooms to go to, who my teachers were, my locker combination.. even though just yesterday I would know. In middle school a teacher approached me and asked me where I was suppose to be, I just looked up in confusion and said “I don’t know”. She looked more confused than I was, and asked how I couldn’t remember my classes and if I were new. I lied and said yes because I didn’t want to be embarrassed. One time, while at a popular festival with hundreds of people walking around, I got lost. I started walking around with MANY people while fireworks went off, and I didn’t feel like I was in the situation I actually was. I felt like I was at a party in 2010 even though it was 2017 and I wasn’t at a party. I could come up with many different scenarios to describe what and where it felt like I was, but none that realistically relates to the situation. This is something different but I only have one question left and I want to ask. Sometimes I will be having a conversation, when I get this weird sensation in my brain. It feels like a tiny vibration, I can still talk and process things, but I feel weird. After its over, I feel a wave of relaxation over my brain and a calm feeling through my body. I will still be able to talk and do things but I feel tired and fatigued. But calm and over relaxed at the same time. An ideas of why this happens? Thanks for reading.