My experience with no sleep happened as a part of 21 day Vipasana meditation retreat. So on the 15th day after constant practice we had to face what they called Determination — 3 days with no sleep, not leaving the room, doing 1hr walking meditation / 1 hr sitting meditation / 1 hr rest, all over again.
As far as i remember the point was to keep all the gained mindfulness and awareness in the counciouness and do not let subcounciouness which acitivates as we fall asleep to kind of ruin the whole practice.
It was an intense process guided by the teacher, with new exercises each day, basically some variations of breath counting.
It was difficult mentally but not so much phisically and after just a night of sleep i felt amazingly fresh.
I like to think that those 3 days of a guided practice with no sleep was the key ingridient to let the meditation become the part of my existense.