Spontaneous:
performed or occurring as a result of a sudden inner impulse or inclination and without premeditation or external stimulus
having an open, natural, and uninhibited manner
Watch a little child play for just a few moments and you'll observe spontaneity.
My little grandson recently discovered his 'talent' for making Donald Duck-like quacking sounds. It's hilarious because he looks so serious when he's doing it, even though we are all laughing uncontrollably. He's just being who he is in that moment, with no inhibitions. What a joy is is to simply observe him smiling, laughing, and being goofy without a thought of whether it's 'proper' or not.
No matter if we are planners or more impulsive, it's a good thing to be spontaneous at times. It will bring out that inner child that needs some fun!