who gets an overwelming feeling of panic when waking?

I don't get this all the time, but sometimes when I wake, I have an overwelming feeling of panic and I find it difficult to breathe. I don't know if it's because I'm fearing the worst before it's even happened, or what, but it's not a nice feeling.. and it lasts for a good few hours after waking. I'll usually throw up for no reason at all towards the end of it, and then it's gone.