I come from a medical family and my father, a doctor, experienced two episodes of ghost visuals. I, being an atheist (only recently), just wanted to share them.
During 70's when my father doing his M.B.B.S., those were the times when India was newly getting it's electrification. For a vacation my father came to his native village to see his parents. We own 2 houses 1km apart and my father stays in the other house. On the way to his parents' home it's all dark and my father is walking, talking with the people coming in front of him. It was around 8pm and a few yards away from the destination, my father casually talked with hands around his close friend in lantern light. According to my father his friend on that day looked a bit sad, but my father neglected thinking him to be moody.
Later next day morning he came to know that close friend whom he talked with hands around is dead 3 days before, i.e even before my father came to the village. My father, during his college days, is an atheist, enthusiastic, adventurous and is also well versed with psychiatry and psychology so I'm just passing this genuine experience.
Second experience also during his medicine days this time a female ghost on the bed. I initially thought his sexual desires manifested that way, but hell no my father said it tried to suffocate him. Only when my grandmom chanted mantras it left. My grandmom used to say it is shankini, one kind of demon. My grandmom never saw a ghost, but she collected many stories from our relatives. Those are not reliable because most of them are cowards. Cowardice may exaggerate the actual experience so don't want to confuse here.