AutoTune makes the copter unstable

Hi, I’ve done the AutoTune twice and my copter works worse after that. Is it normal? What am I doing bad? Before the AutoTune everything works pretty ok, maybe is not so precise as I wish but it is stable. When it passes the AutoTune, the copter become really un
stable and it fells down. Any idea? Should I flight it without AutoTune?
Thanks!

If your copter flies well without autotue fly as it, but if you need that others check your autotune, it´s better if you share your autotune log.
You follow the instructions here? http://ardupilot.org/copter/docs/autotune.html#autotune

as cala2 says, log would help, but check for bad vibrations or supersoft AP mounting.