I remember watching this interview about this guy who had to be resuscitated and he said that what he felt was "nothing", as in kind of like when you're sleeping and you know nothing, except turned up to a thousand. He said he had to go through some serious therapy to get over it because when he "came back", he just couldn't believe that he had lost that sense of not having anything to worry about. I would venture its something like that, just like going to sleep but you just don't even know it.
If we assume that all we are is just electrical impulses in our brains and those cease when we die, I don't expect there to be much after that, you're just gone and there's nothing, so there is no suffering either.