spontaneously
adverb
[ spɒnˈteɪnɪəsli ]
• as a result of a sudden impulse and without premeditation.
• "the crowd spontaneously burst into song"
Similar:
without being asked,
of one's own accord,
voluntarily,
on impulse,
impulsively,
on the spur of the moment,
extempore,
extemporaneously,
off the cuff,
