lol ok that's funny. But to be serious, yes I see them...and no not on drugs. In fact that side of shuts done when high.
They can't harm you and most of the time what you see is not a spirt...is more like an astral shell...or residual energy if you like.
True sensitives can pick up on sentient spirits and most often, they're not really happy. They can be waiting on for their loved one to pass...a misguided sense of responsibility that remains from before they died. Or they can be attached to a place. Those ones are often fucked up versions of what they were when they were alive and pretty much ooze anger. they will fuck with your head if they find away to communicate...usually they don't and you don't know they're there.
Oh...the last type I've seen are kids. For some reason they are tied to a place or person in a way spirits of older decseases re not. They usually want to play...and will play. One I encountered in a friends house would jigle the locks every time I came over cos she was excited I could see her. She'd run out the front and play in the yard at dusk. Felt kinda sorry for her actually.