Once sent my RAF IRE to sleep during a limited panel U.P. recovery in a JP5 (Altimeter, ASI and Turn and Slip only). After he flew a few U.P. gyrations, including positive and negative G, during which he insisted I had my eyes shut under my IF hood, he craftily gave me control inverted, just after the apex of a barrel roll. I held 1G and "levelled the wings", iaw with the recommended recovery drill. I watched the altimeter, which began to unwind, so I pulled back on the stick to stop it. As we were inverted and pulling into a vertical dive, it unwound a lot more - so I kept pulling. I suddenly twigged what he had done, but by then it was too late to roll the correct way up. I continued to pull to just under 7G to stop the altimeter unwinding. As we went past about 6.5G, his chin suddenly snapped down onto his chest and he was out like a light......
By the time he woke up and started twitching, I was at full power and climbing like a dingbat. He was silent for quite some time. I levelled off, and he said "that was enough of those" and to go home for the ILS.
He never admitted he had blacked out and I passed the IRT!