Is imagining seeing nurses in the dark and hearing them talking to you a sign of a brain tumor?

Not necessarily. The kind of problems you are describing can be attributed to many kinds of medical problems. I would suggest that you see your family medicine or internal medicine physician to discuss what is happening, give a complete medical history, undergoe a complete medical exam which will probaby include some blood work---and then this can be more accurately assessed. Many causes can explain this.
Completing answer. I was finishing the answer, and suddenly screen disappeared, don't know if published. But the up shot is that this person is experiencing an auditory (hearing) and visual (seeing) hallucination, presuming the nurses r not actually there. This is either some type of dream state, a form of delirium, or--most likely--exposure to a mind-altering drug, such as marijuana/cocaine. Not a brain tumor.