Good morning!
There is a TV series on the Biography Channel titled "I Survived, Beyond and Back" in which people relate their near-death experiences. The few that I have watched seem to run the gamut - from vivid descriptions of Hell to various concepts of Heaven.
My opinion on this may sound somewhat wishy-washy, but here it is: As a mature Christian, personally I see no problem with it. It's an entertaining program, but I am certainly not going to base my theology on it.
I haven't seen enough of them to form an opinion, but they may air episodes that conflict with Christian teaching. That would be problematic for new Christians or non-believers.
Your agnostic friend asks a good question, and to that I would reply to always be skeptical and use caution where extra-Biblical things are concerned. We can say with 100 percent certainty that what God wants us to know about Heaven and Hell is contained in Scripture. Anything beyond that is pure speculation.
Have a Blessed day!
-Ed