My deepest dive was to 36m on air. Total divetime 6 minutes... We were diving a wall and the dive included me, an "advanced" diver with NO concept of buoyancy. Short story... he sank like a rock before I managed to grab his tank at 36m. My problem is that the faster I decend past 25, the faster I go into dark narc. I am very aware of it, so normally I control my pulse and resps very well. However, pulling up a very negative diver from 36 was quite the ordeal. I got him to 22m, levelled off, gets an ok from him, and the first thing he does when I let go, is to vent his drysuit. I caught up with him at 31m. He then had a freeflowing 2nd stage, and we ended up doing a nostop ascent to the surface.
Quite scary. Normally I stay within 30m, and usually above 20 as it is dark, and cold here in Norway.