It's possible that there might be some confusion here as to the nature of the experience. Sometimes in a moment of intense prayer and soul-searching, it's possible to experience something that's kind of like a moment of clarity: you know with full conviction that something is correct. I'm somewhere between an agnostic and a deist myself but I have experienced this a few times at some of my most spiritually and emotionally raw moments. I believe it is an experience like this that people interpret as a message from God, although I also believe there's a perfectly plausible psychological explanation as well. I suspect your friend had one of these moments of conviction that he took to be a spiritual message. Might be true, might not. I wouldn't worry about it as a sign of psychological imbalance, it just means that, based on his world view, he interpreted something in a certain way that is different from yours. As for the message that Christ is in your heart, I agree with the others in saying that it partly just means he cares about you. There is a degree of putting his beliefs onto you here but, then again, that's the nature of a belief. Your religious friend sees the world in a certain way and so do you, the only thing to do is accept it, respect it without judging, and move on.