My second baby is due in 9 days and I am trying not to think about it! I just want to send you my support.
You're not odd, this sounds completely normal to me. Of course it is natural to worry. Lots of women have great birth experiences but, then again, giving birth can be mighty painful (and anybody who tells you otherwise is either lying or has forgotten! - after the birth, we tend to forget almost immediately how awful it was because we are so wrapped up in our gorgeous new babies).
Some of the women who worry the most actually find that they cope really well during delivery. Still, there comes a point in many women's labours when they say "I can't do this any more / I am going home" and, at that point, the midwives smile to each other because it is a generally a sign that the baby is imminent and everything is going well.
Your body is 'designed' to do this, despite your high-risk pregnancy. Yes it hurts, but lots of us have been there and can tell you that it is worth every second. Labour pains are strong but very different to the kind of pain that you have already been through - I think we have some sort of inbuilt way of dealing with labour pains or, as BoysBoysBoys says, we wouldn't keep on choosing to do this again and again.
Jojoba is right in telling you not to dwell on it but of course, if you are having nightmares, this might be difficult to control. There is every chance you will be fine, and that all this worry will seem ridiculous to you in three month's time.