YES and I have seen proof.

Spoke to my SO's ex-boyfriend's spirit in my sleep. He's been dead for over 10 yrs at the time. She would have dreams with him telling her that she has forgotten about him ~2 times a year.

I never knew him. In my dream it was all black but I felt a presence. He spoke to me and I felt all of his pain and grief throughout his lifetime some how. He told me that my wife was a "good girl" and to "take care of her". As I realize who I was talking to, I said "This is crazy! You have to tell me something that only she would know to believe that we've spoken. He kinda laughed and told me a fairly descriptive story of an event that took place on a particular block..

As I realized "Holy sht, I'm really talking to a spirit!". I thought to myself, I had to ask him one of the most important Unanswered questions of mankind. "Is Heaven real?*"... And for some reason as if he anticipated the question he disappeared and turned into a bolt of lightning.

Than I awake. Told my wife to wake up because I think I just spoke to her ex. She laughs and says why do you say that. I told "I'm serious! He told me about that big rumble that he got into over you in a house party on such and such block." Her face turned pale and she said "wtf, how the hell could you know that, I never told you?!" I replied "I know! That's because I asked him for proof that we spoke".

So my wife gets off the bed a little while later and checks her phone's notifications, and there is a text that said "*You forgot about me? *. (crazy right?!) it was a message from the brother of the kid that was killed. Turns out, a few weeks prior to the dream she ran into him on MySpace and he wanted us to help him with buying a home (we're in real estate) , Hence, the message" you forgot about me".

My wife called the brother the next day and told him "my husband had a dream with your brother" and he said "that's crazy. Because me, my mom were reminiscing about him, drinking and crying last night going through the photo albums. And something just came over me and that's when I thought about and decided to text you last night".

This event has changed my life forever and left me in a state of shock for a few weeks. That's when I started looking into meditation and astral projection to try to gain that ability again. Never happened again though.

There is more to the story but I'm on a phone and wanted to keep it as short as possible.