Ever heard of Lucid Dreaming?
The brain is very active during sleep and a hell of a lot more powerful. Through practice (or accident) you can indeed become 'concious' during sleep.
If I asked you right now to imagine and actually 'feel' what it's like to fly, or lay on a field of grass with all the individual blades of grass poking against your back, I'm pretty certain you couldn't, the concious part of your brain can't process such vast information. Yet during lucid dreaming you can do this easily and even feel it as though it is actually happening.
A common example I suppose would be that feeling most people have had of falling then suddenly waking up, your body obviously didn't move from your bed, yet your mind convinces your body it was real and to feel it.
We always have these kind of conversations at work, or should I say I bore people with talking about it
I think memory plays a huge huge part in our being. Assuming you don't know how to become concious during a dream, you live out that dream as though that's reality, it's only when you awake can you comprehend that it was all just a dream. It's like a switch in your head, when the dream light is on you're whatever you dream says you are, but when you wake that light turns off and the 'reality' light comes on and suddenly you're a completely different person.
Is it not a possibility that when we die we could also 'wake up' and be a completely different person/being and only then comprehend that our physical life was just a dream?