Why do I see dead people?

For some reason I keep seeing this dead girl everywhere. she makes me drown in my dreams and she watches me. I looked her up and found her on the internet. When my gma was dying i saw her looking at her and i looked at my gma and could tell she saw her too. she attacked me then and i was practically having a seizure in the room. I cant remember what was happening but I do remember holding my gmas hand and everything was black. I could feel water filling my lungs and it burned so bad. I heard my already dead gpa helping me through it. Can you plz help me? I feel alone =( and I am scared.