Are people that claim to have been visited by the dead hallucinating?

Have you had any experiences? I’m not talking about a dream either. Seems many people claim that in a dream or when they are just waking up which is probably likely still dreaming.

What theory does science have for those who have claimed a loved one has visited them other than thinking it’s a lie or that they’re crazy? In some stories, people claim something that is pretty eery. One story of a woman talking to a man she’s always given advice to and is pretty close with and him saying goodbye only to have her find out he was pronounced dead a few hours before. Something like that. But many non believers say it’s just wishful thinking and it’s all made up in their head due to the stress and traumatic experience.

Is it just coincidence, in our heads, or something spiritual?

Also, why do some people feel that a loved one has visited them but no other loved ones, why doesn’t everyone experience that? I mean, what’s the purpose anyways? If they did have the option to give their last goodbyes, why doesn’t everyone that has died do it ya know?