try this:
Pretend to the best of your ability that you are willing to go asleep at that very moment.
Sleep is a program deeply embedded in our brains - when we lie down and decide to sleep, we send the brain a certain signal.
Try reproducing that signal as you're meditating in your favourite posture and this will effectively fool your brain into thinking that you are planning to sleep, so your brain will slow down brainwaves while your mind stays awake.
I've struggled for the last few months under the wrong notion I had, which was: "when mental activity is lowered, the body will begin to shut down and the physical mind will fall into trance". WRONG!
No matter how hard I focused and focused on ignoring intrusive thoughts, my brain would still be rolling and and firing up neurons to the nines which basically means - no chance in hell.
Not even my beloved third-eye focus trance induction method would work anymore.
So fooling my brain into assuming I'd be willing to sleep is the only truely reliable method I've found that promises a falling into trance will occur.
Great success to you all and stay the course!
peace