Welcome to DreamViews.

To your fears:

•You said that your dreams are not very clear, there are several things you can try to increase clarity and realism:
-spinning
-rubbing your hands
-shouting "Increase Clarity"
-Use all of your senses (Feel, smell, listen)

•Getting a nightmare while being lucid is rubbish as a fear, because having a nightmare in a non-lucid dream would be worse, as you have unlimited power in a lucid dream you could kill or run or teleport or whatever to end you nightmare.

•You can actually do like STUFF. By the way a lucid dream is a dream in which you KNOW IT'S A DREAM. If you think it's reality it's no lucid dream. If you don't know what's possible in a ld, you may check out the LD Experience Checklist by toomanypossibilities.

•You can DEFINETLY NOT die because of a dream, as it just is a creation of your mind. To talk from experience, I "died" already several times in a lucid dream, nothing happend to me, not even in the dream. It did not even hurt.

Cheers
Thorim