I have had that scared/nervous feeling...at some point it stops being a problem and just becomes normal. At least it did for me.
I remember thinking how cold the people involved in my first code were too, but after a while you learn that the joking and laughing is just how many people learn to deal with such things. Now that should NEVER be done with family around...
I have had a few students tell me they couldn't wait to see someone die, or couldnt wait to feel the ribs break. Those students concern me far more than a student who is nervous/scared.
The dead body issue is something that hopefully will pass with time. You realize that it is just a body, there is no person in there anymore. It is just their earthly core.
If you are really concerned find an instuctor or preceptor that you trust and talk to them about it.