"Unplanned" generally means "without though, accidental or unintentional." Examples of use are "Carol's was an unplanned pregnancy;" "Our meeting at the airport bar was quite unplanned;" "The group's removal to the third floor came off well despite being largely unplanned."
There is a medical term "assident" (meaning concurrent disease symptoms). A more common term is "accident" (an unplanned event, e.g. car crash).
Irregular patterns are natural repetitions that appear to be unplanned or unorganized.
It was a Battle of Encounter, meaning it was unplanned, accidental.
What is an unplanned economy
Offhand is the odd term because it has nothing to do with unplanned actions.
Unplanned.
This is unplanned.
This side trip was unplanned, but enjoyable.
The term that is defined as natural repetition that appears to be unplanned or unorganized is "echolalia." Echolalia is a speech disorder characterized by the involuntary repetition of words or phrases spoken by others. It can be a common feature of autism spectrum disorders or other developmental conditions.
it has a mixed economy
odd, irregular, accidental, chance, haphazard, casual, incidental, stray, unplanned
Impromptu is the closest to spontaneous word. It is a word representing sudden action.