I See Dead People

Hello. I just had a dream lastnight that involved somebody I knew that was deceased for about a year or two. She was my Spanish teacher for two years and we had a friendly student/teacher relationship but we never talked all that much. I was saddened by her death because I respected her but also thought that she was a very nice person as well.

The setting of my dream placed me back at school(I have been graduated for close to a year). I was sitting in what appeared to be my chemistry room. I was learning about something unimportant when a nurse, two ladies I did not recognize, and my Spanish teacher were all standing in the door way. That's when the nurse told me I had acute lung deficiency disorder which I never even heard of and I looked it up and couldn't find anything. I noticed sometime before that that I was having trouble breathing and my chest hurt a little but it felt more like a chest cold.( Which I do not have right now in real life).

I never talked to my teacher in the dream but me and her looked at each other for awhile and I knew that she was supposed to be dead. Then that was it. I woke up.

Could anybody tell me what this signifies? Seeing a deceased person that you knew in a dream?