also could have been the moment right before the blade flapped up into the other. ^^
I guess the problem was probably either trim reset (strg+t) oder something with you autohover, but hard to find out without a track.
I don't know why your nose pulled up, even if I suspect trim reset. But the lovely kachunk is the sound of colliding rotorblades :D No wonder why you lost control of the cyclic, without blades... :)