Is it normal to see people that aren't really there?

You might want to google pareidolia, which describes the way the brain continuously attempts to make sense of patterns.

Most of us will have come across the phenomenon when out in the twilight, one's brain and eyes create images (usually human figures) from patterns in the half-light. When one gets closer, it turns out to be street furniture, or an oddly-shaped shrub, or merely shadows.

"I see dead people."

.....Haley Joel Osment, the haunted little boy at the center of the supernatural thriller The Sixth Sense

Well they use to call booze spirits the reason why is you would see spirits dead people your late relatives so keep drinking spirits