Thank you for your answers
My fears are getting smaller by the day and I think I'm soon ready for a serious attempt.

One more thing: Can I avoid visual hallucinations by simply keeping my eyes shut?

MBA42: I really don't know if it was SP, because I could move right after I heard the sound. (Maby I snapped out of it) But I got to that point by laying in a comfortable position (On my stomach with one arm under my head) and just focus on my breathing with an empty mind.