Since I posted my e-mails to MC in here, may as well include his reply (going back to all three e-mails, hence the first part), which I found to be very caring and understanding:
"Hi LT,

First and Foremost, I do not have any illnesses that I know of, so I am not worried that I will die in three months. (Notice I did not say that I was ok.).

I know that you made yourself vulnerable with this e-mail and I agree that shows progress. Good job. I also don't see you as immature or acting like a 4 year old. It is ok and helpful sometimes to discuss some of these formative fears and feelings. Nothing immature about it.

We probably should continue to talk about security, including the sense of security you feel in sessions with me. That too is an ok topic. You are right, even though this sometimes comes up in regards to me, on a deeper level, it goes back to other formative relationships.

See you Monday."