One thing I have noticed in some friends I have when they do not break through is that they seem so apprehensive and feed into their trepidation by allowing the mind to influence their trip.  I noticed they would not inhale quite enough or hold it long enough.  As if they do not actually want to go.  Like lining up to get on a roller coaster and chickening out at the last second.

I am not saying this is the case for everyone or for the OP.  It is just something I have noticed with people who claim to not break through over the years.  I think if you have it in your mind that you want to have the experience, you will do what you need to do to get there.  All to often I think people simply hold themselves back.  Perhaps they are not quite ready for it.  It takes courage but more so an explorers mind.  Wanting to go and see.  Jump in and you may wonder what all the worry was all about.  Worry is a waste of time and energy.  Everything will be ok.

I get nervous and have some anxiety before a trip but I look at it as excitement.  Like jumping from a plane. Just jump!!