Over the past few days I’ve been trying to have ludic dreams but I’ve been too scared to sleep, in case the dream gets out of hand and I’m plunged into a nightmare; is this normal?
Hi regirock, welcome to LD4all! 
Yes, don’t worry, this is normal. The main way to combat this is to try and relax. Tension and anxiety can cause nightmares, so try and release these thoughts while getting to sleep. If you do happen to get a nightmare, (sorry to unnerve you in any way), don’t let it stand in your way. It is a dream after all. Be confident, be brave; you might even be able to conquer your nightmares! Believe your nightmare to be something else. If you do succeed in conquering your nightmare, you’ll never get it again.
If you have any more questions, just ask. 
Your main obstacle is belief. If you believe you could have a nightmare you will be un-relaxed and more likely to have one. But if you can force yourself to believe that you will have a wonderful dream you’re very likely to. Just as you must believe that you will have a lucid dream. Never doubt it for even a second and you should be lucid dreaming in no time.
And remember to relax.
Welcome to LD4all. The people here are extremely nice and always willing to help, so don’t be afraid to ask.
Dreams can’t hurt you. The only thing you have to fear is fear itself.
(Yes, I know it’s a cliche).
This reaction is quite normal. There was a long thread about this:
Too scared to LD
Normal dreams are more likely to get out of hand than LD’s. And since I’m reading first LD’s, I never saw any nightmare. I just remember a girl on another forum whom first LD’s were a bit frightening. But she was very tenacious and she wanted to have LD’s, so in her fifth LD, she decided to find a bazooka under her bed in order to shot monsters. The monsters were less courageous than she was, cause they never came again! 