If you want a medical explanation, you may have been experiencing sleep paralysis.
Sleep paralysis - Wikipedia, the free encyclopedia
A lot of people have experiences like you describe while in that paralyzed state between waking and sleep, and swear it seemed real as day. It has something to do with the mind being awake while the body is asleep.
That said, I don't know what
you experienced, but this explanation might give you peace of mind.