I have a lot of experience and this still happens to me sometimes. There are an unknown number of unknown variables that may prevent success. Just don't let it get you down.

Once you reach SP don't worry about accidentally losing consciousness. Reiterating what Sanctum said - Just let go of your body and wait for the dream.

May I ask exactly what kind of sensations you're feeling when you reach SP? Do you feel any sense of movement like floating or being pulled down?