In his book, The Devil and all his works, Dennis Wheatly writes the following:
"Having had Crowley to dinner several times, I told my friend Z. that, although I found him intensely interesting, I was convinced that he could not harm a rabbit.
"'Ah!' replied Z. "Not now, perhaps. But he was very different before that affair in Paris.' THe affair in Paris was as follows.
"Crowley wanted to raise Pan. One of his disciples owned a small hotel on the Left Bank. Crowley, with his twelve disciples, took it over for the weekend and the servents were given a holiday. On Saturday night a big room at the top of the house was emptied and all of its furniture, swept and garnished. Crowley and his principle disciple, MacAleister (son of Aleister), were to perform the ceremony there, while the other eleven remained downstairs. He told them that, whatever noises they might hear, in no circumstances were they to enter the room before morning.
"Down in the little resteraunt a cold collation had been prepared. THe eleven had supper and waited uneasily. They all had a great deal to drink, but got only stale-tight. By midnight the place had become intensly cold. They heard shouting and banging in the room upstairs, but obeyed orders not to go up. In the morning they did go up. The door was locked and they could get no reply to their anxious calls, so they broke it down.
"Crowley had raised Pan all right. MacAleister was dead and Crowley, stripped of his magician's robes, a naked gibbering idiot crouching in a corner.
"Before he was fit to go about again, he spent four months in a lunatic asylum. Z., who told me all this, had been one of the disciples, and an eye-witness to this party."
Sounds like a sensationalist tall tale to me, best taken with a large pinch of salt - I think the true events were probably closer to what Ged said.