Every time I fall asleep and start dreaming I have no recollection of the fact that just a moment ago I was in my bed falling asleep. I will be unaware of my dreaming condition and I will be fooled by the veracity of the dream believing that it is reality. My memories of previous days will be in agreement with the circumstances of that dream.
Tomorrow, after waking up, my memories of the past will be in agreement with the circumstances of that new day and I will be convinced that a few hours ago I just went to sleep.
How can I be sure that at that moment I will not be having a new dream?