Is this something serious or just in my head?

Why do I get these sudden almost deja vu like spells? I will be sitting somewhere, or standing, or laying down and all of a sudden I will feel this weird feeling, it feels like what I would describe as almost like deja vu. I can always sense when this is about to happen like sound will start to muffle just a bit and I will get a bit light headed. Then BAM I feel so weird. I always become very nauseous during this, half the time I actually throw up but I always make it to the toilet to throw up, like I can hold it long enough to do that. After a few minutes it goes away and I feel almost better than I did before. I am not crazy I promise, I know this isn't deja vu. It just feels like that weird feeling. I really think there is something wrong with me it can't just be all in my head. I have never told anybody about this, it has happened around my mom but I told her I just fell nauseous sometimes. I'm afraid to tell anybody because I don't want them to think I am crazy. I've had this for the past four or so years so it isn't anything new. What could this be?