I've had very similar experience - a dream that turned into horror (I was visiting family when I remembered my grandpa is dead and they all turned into zombies

I've had very similar experience - a dream that turned into horror (I was visiting family when I remembered my grandpa is dead and they all turned into zombies and started pursuing me) - then I "woke up", sit up in my bed (and my room mate seen me sit up with open eyes), I looked at him, and he turned into a zombie and attacked me, then I woke up for real, already siting. It was very scary. It might have something to do with the fact that we were studying before an exam late into night and I drank about 2 liters of pretty strong tea to keep studying (and fell asleep anyway eventually).