When we come up with something on the spot, we often describe it as being "made up off the top of our head." This kind of spontaneous creativity can be exhilarating, but sometimes we need to be more thoughtful and deliberate in our approach. Antonyms for this phrase might include terms like deliberate, intentional, planned, calculated, or premeditated. These words suggest a more thoughtful and structured approach to problem-solving or decision-making, rather than relying solely on instinct or intuition. While both approaches have their advantages, choosing the right method often comes down to the situation at hand and the desired outcome.