It's the first jump to mount the rail that scares the shit out of me.
I have a gymnastics/tumbling background so I'm used to jumping around on stuff but when there's a 500kg board strapped to my foot, EVERYTHING changes.
Getting off the rail or falling off it is easy peezy; it's that first moment of jumping onto it from the side where things usually get really ugly.
Being afraid of that type of feature is just something that is going to take a little bit of time and a few committed trys until you get the hang of what you need to do and aren't afraid to approach the rail. After you actually try it a few time you will get comfortable with features like a hop on rail and will be able to really get working on it.
Here, this is a recent thread on this topic and has some good info in it.
My first post in there sort of covers it. One of the biggest things everyone else said that i totally forgot to mention is that when you are on the rail make sure you are looking torwards the end of the rail and past that. That will keep you on the rail longer and you will have better balance.