I do believe there is a concept of shadim/dibbuks/and when a neshama is still “lingering” after its petira on Olam HaZeh.
I remember when my great grandmother was niftar (On Friday- On her birthday) she m,ore “appeared” to me then in a dream- it was so surreal (i felt as though she was literally in the room) She told me some things to take with me for life (I was only 8)…I was so freaked out, during the week of shivah I was acting really strange…later on I found out a lot of my family members (grandmother, aunts n uncles) were visited too.