Or you could do the breath hold after inhaling nitrous oxide. I have not tried that yet with subliminals, but just doing it with the breath hold is quite fascinating. I had my mind coming up with sounds and sights that were totally made up to make me breathe in again, and as soon as I realized this I could call the bullshit and things became quiet again.
One time when at a bar doing some ballons of it I even felt being physically slapped where I felt the hand imprint long after on my cheek. My friend was sitting next to me and when I told him that he was like WTF that did not happen lol.