Spontaneous
Unforced
Synonyms: Unforced, unconstrained, unbidden, unplanned, unrehearsed, impetuous, impromptu, extempore, unschooled, uninstructed, voluntary, unprompted, unsolicited, unpremeditated, impulsive, unstudied, spur-of-the-moment, extemporaneous, untaught, and off-the-cuff.
Natural
Synonyms: Natural, relaxed, unaffected, free and easy, impetuous, genuine, uninhibited, unselfconscious, easy, impulsive, and open.
Reflex
Synonyms: Reflex, knee-jerk, unthinking, instinctive, gut, automatic, involuntary, unconscious, and instinctual.
Example Sentences
Their spontaneous trip was a success.
She enjoys spontaneous adventures and experiences.
The crowd erupted in spontaneous applause.
He made a spontaneous decision today.