I remember trying this some year ago when a lot of bloggers were trying it out and blogging about their experiences. I tried the Uberman Sleep Cycle (4x15min) but inevitably it wore me down to the point of being completely nonfunctional.
- I gave up caffeine the month before the trial. I had pretty significant withdrawal effects (migraines) for that month.
- I was pretty much completely non-functional for about half an hour before the scheduled nap times
- I didn't think I was impacted very much, but friends commented after that I definitely seemed less bright than normal. I hope that it was for the half an hour mentioned above, but if you want to try it you should definitely try and get some objective measurement of performance.
- I still notice effects to this day. I can nap pretty much wherever & whenever I want, and fall asleep within minutes of my head hitting the pillow. Before the trial, it used to take me hours to fall asleep.