I Want to Know

What is extreme deja vu? Every now and then I get the feeling that the current situation I'm in has happened before. It's kind of weird but no big deal because I'm use to it. Lately though I've had them and have a taste or smell that comes out of nowhere and absolutely overwhelms me. It floods all my senses and seems so totally familiar like a huge part of my life. Then it's gone. For maybe a minute I'm in shock at the memory of it and then even the memory fades. I dont know what this is.