Hi Henry,
My experience of
magga/phala is that preception disappears quite suddenly then also reappears just as suddenly. The first time I had such an experience, I was buying gas in LA after a retreat with Shinzen Young. I came out of the gas station after having paid, put my hand on the door handle of the car, and the next thing I realized I was sitting behind the wheel of the car staring at the dashboard with no memory of having climbed into the car. There were a few seconds when I got into the car where perception was shut down. I've had similar experiences a few other times, but not often, and they have always been during or after very intensive retreats (Shinzen's retreats tend to be quite intense). I've also had
magga/phala experiences both while in meditation and while walking around.* In addition, I've found a
magga/phala experience tends to be followed by a tremendous upsurge of energy, almost like kundalini but not painful, more blissful. Many other practitioners report this too.
In contrast, in a
sarvopalambhopasama experience, perception seems to gradually fade then gradually return and it only happens during meditation. It seems to be a result of cultivating a view of emptiness around perception of a particular sense; in my case, the body sense, but according to Burbea different people will find different senses that work for them. For me, there's also not the tremendous upsurge of energy afterward, just a quiet feeling of comfort and ease. Actually, when it first started happening, I thought I might be falling asleep, but there is a definite difference, in that your muscles don't lose tone and you stay in the upright sitting position. When I start falling asleep, I end up leaning forward and then have to catch myself or wake up with my face on the carpet. That doesn't happen with
sarvopalambhopasama, just like it doesn't with
nirodha samapati or
magga/phala. I puzzled over this for about a year, until I encountered Burbea's book.
*Shinzen tells a story about driving across LA on the freeway and going in and out of
phala. Given the LA freeway traffic, not something I would be eager to try.