I had a premonition before one of my friends (now boyfriend) grandmothers died. Actually it was his only grandmother but it was the wrong person. I had a dream that my friend had died, as opposed to his grandmother. I wake up that morning thinking of it and my mother tells me that Betty (his grandmother) had died. Was it some sort of coincidence? I think it might've been because my own grandmother has since passed on and I had no premonition before her death, though she was in the hospital for months before.
Maybe your mom told you while you were groggy, and you went back to sleep. So she decided to tellyou in the morning.