If you get more than one insanity during an act, you add tokens to your current insanity. At the end, you check and see if it's permanent with a WP check.
It doesn't say if there is a difficulty for the check, or if it is just a WP number of dice roll. It says you have to get a number of successes on the roll equal to the number of tokens. Does it mean, the number of tokens + the severity rating?