Try to get more information out of him before you take him to the docs. But maybe he's clinically depressed - it is possible, I've observed it
Hi. Well, eight year old boys talk and perhaps someone at school talked about heaven, or has a grandparent that got ill and died or a sick parent or sibling, etc.He could have seen something on tv, overheard a conversation, etc.
At this point, I would not panic or freak out. Instead, encourage dialogue with him so that he feels safe to talk to you about emotions.
Being suicidal is something that stems from depression. Has he appeared to be depressed to you? There are signs and symptoms and if you aren't sure what they are, I can tell you.
Being suicidal is something to take seriously. BUT, this is more than a child simply saying something like "I want to kill myself". Many kids do that for effect or in the heat of a moment. But suicidal ideation involves picture one's death and how they'd do it. When this is suspected, it is a medical emergency and a parent must seek treatment for their child immediately.
It doesn't sound like this to me from what you describe. He sounds like he is thinking about death and mystified by it a bit. That's okay. Keep conversations going. I know it is hard to listen to as a parent--- but remember, he feels he can just 'talk' to you and that is all he is doing is talking about something on his mind. My thought is again, something put these thoughts in his mind. I wouldn't go too crazy trying to figure it out as you may just reinforce the thoughts.
Get him doing some fun things right now and work on any self esteem issues he may have.
And if he does appear to be depressed, start some counseling to begin addressing that.
good luck
Maybe its best to take him to the hospital get a full exam, xrays and ct scan. He may be speaking crazy but he may know his body. Just to be on the safe side tkae him in