[Meditate]

I have been practicing yoga nidra for about 8 years in order to overcome depression and anxiety associated with PTSD and chronic back pain.
Recently I was reading a novel where the protagonist did a week long meditation course which culminated in a practice where participants were invited to imagine their physical bodies floating away, atom by atom.
I didn't think I would be able to achieve this state but found that after my normal meditation I was able to visualise this. Immediately my pain disappeared, no physical body equalled no physical pain. I also experienced a high that was as intense as serious painkillers such as OxyContin. The high lasted for hours and the pain was gone for days. I was able to refresh the feeling the day after I first undertook the meditation but haven't been able to achieve it since. I think I'm focusing on the outcome more than the process.
Has anybody else tried this meditation and/or had similar experiences?