The phrase 'did top of your head' typically refers to something that is done or said without any prior preparation or thought. Synonyms for this phrase may include off the cuff, impromptu, spontaneous, ad-lib, extemporaneous, improvised, unprepared, unrehearsed, and spur-of-the-moment. These terms all suggest a degree of spontaneity and improvisation, as well as a lack of premeditation. These phrases are often useful when discussing a particular performance or speech that was delivered without any prior planning, or when referring to a spontaneous reaction or decision that was made in the moment.