How do you know if your going competely crazy even if you dont want to?

how do you know if your going completely crazy even if you don't want to? your imagination goes a lot more psycho than you let it be, you don't want it to go any father than to having to imagine Boogie man under your bed but your imagination does, you don't have control over it anymore you want it stop but it keeps going...how do you know you've already gone crazy?