Sudden : leaerning in the tube

On the spur of the moment (Words and phrases to describe sudden actions)

• An impromptu event is not planned but it happens right at the time: The singer gave an impromptu performance at a restaurant in Paris last week.
• something that is done ad hoc is not planned in advance but it is required: We deal with problems on an ad hoc basis (=as they happen). ‘Ad hoc’ is also used as an adjective: an ad hoc committee
• If you do something without planning or thought beforehand, you are doing something on the spur of the moment – spur-of-the-moment decision.
• Of course, some actions are reflex action , instinctive response – you are automatic, instinctive and involuntary.