Expectations are everything. If you're afraid that you're going to have terrifying hallucinations, chances are that you will because you're focusing you're thoughts on them. My first SP experiences were very noisy. Why? Because that's what so many other people told me. After some time, they quieted down. One guy gave an account of seeing flashing lights. Then, surprise surprise, the next time I had SP, I saw some.

Now I usually just feel a general heaviness and relaxation in my body. It's a pleasant feeling. You could imagine having an experience like that instead.

And also remember, SP is very harmless. Just relax, and you'll be fine.