When it comes to finding synonyms for "did off the top of head," there are a variety of phrases that can be used. One possibility is "performed from memory," which implies that the action was completed without the aid of external resources. Another synonym is "recalled from memory," which suggests that the information was retrieved from one's own mind rather than from written notes or other sources. "Spontaneously completed" is another option, indicating that the task was done without pre-planning or preparation. Overall, there are many ways to describe completing a task or recalling information without external resources, each with its own subtle nuances.