Insanity spell makes the target permanently confused.
A very flavorful way to get rid of an enemy, a bit marred by the fact that pathfinder confusion table includes self-harm, so 'permanently' is very unlikely to last more than ten minutes.
So, here is the question. The self harm result is "deal D8+str modifier to self with item in hand" and victims who can't do what the roll says just waste a turn.
If a character has no "items in hand", will he be safe, or do you have to literally straight-jacket him to prevent him from clawing at his own throat?
Rules-wise (because this is Rules), it's like the others say. Basically you're going to have your chance to inflict self-damage. Obviously if they're barehanded the damage should be non-lethal, but if the character were wearing (or had someone else place) boxing gloves or had oven mitts on their hands I might lower it. But that's due to the wording about using objects in their hands.
Certainly they could be slamming their head into a wall or the ground, but sticking with the wording such a case is within a GM's purview. Otherwise, you might get a situation where that roll not only causes the victim damage as worded, but now they're prone or kneeling because they had to slam their head on the ground and that isn't implied.
Personally, in my game I have a loose house rule (because insanity or permanent confusion hasn't come up a lot, and when it does it's on a player), I've restricted it to stressful situations. Combat, obviously, but also any serious roleplaying or intense encounter. It's just been easier that way to not assume I have to roll 10 times a minute while otherwise things are peaceful. At any important time of interaction or a scene (even a peaceful one, like when you find the healer to cure you), I start rolling again. But that's just been how I dealt with it, that it only triggers in 'situations'. I can let the character sit in a chair for hours or painting, but maybe only make one or two rolls for an episode of confusion.
Well, if bestow curse can afflict folks with different kinds of curses, then maybe insanity can bestow different forms of confusion. Remember, custom curses can't be stronger than those listed, so I think it should be the same with different forms of confusion.
I think 01-50 act normally, and 51-100 babble incoherently would work if you didn't want the victim to kill themself. It'd also let them to be sane enough to recognize that half their time their mind is broken.