A childhood belief about sleeping

I had problems with nightmares when I was younger and everynight I would repeat "There's no such thing" over and over again hoping that I could convince myself. But I guess my sister who slep in the bottom bunk got aggrivated with my muttering at night and told me that it was no use. That I was too smart for my own good, that I knew the truth. That there was such a thing. And my sister was always so mean that I thought if she was actually calling me smart that she must be telling the truth. I don't think I had a nightmare-less night for a month. I was terrified to sleep. I never really connected the dots that when I used to mutter to myself - it actually did work.