When it comes to speaking off the top of your head, there are many synonyms that can be used to convey the spontaneous and unrehearsed nature of the conversation. Some common alternatives to "doing off the top of head" include speaking impromptu, improvising, extemporizing, freestyling, and ad-libbing. These terms all suggest that the speaker is making things up on the spot, without any prior preparation or planning. They can be useful for describing conversations or speeches that are particularly energetic or spontaneous, where the speaker is relying on their natural talents and instincts to guide them through the discussion.