I have nodded off when hand flying. I had taken a piston single for a 50 hour check first thing and sat on the near by beach for a few hours while it was done. Late afternoon, flying home with beautifully still air, aeroplane sitting there perfectly trimmed, I may not have been 'asleep' but was certainly not in the cockpit! I recognised my call sign and came to with a start! I think I was probably out of it for 5-10 minutes. I'd been working a fair bit previously and I think sitting in the sun wiped me out. Luckily not literately! I was only at 3000' and the aircraft was quite slippery; imagine waking up in a steep spiral dive with the last few hundred feet winding off the altimeter! Should have recongnised the potential problem before take off, I know, but everyone's perfect with hindsight...