The tip of the pyramid, or the ice burg (it's what's underneath that you get caught up on), self actualization rests on Maslow's hierarchy of needs. In lecture, we learned about "Flow" and how different types of people (ie. writer ceases to exist when writing, I believe it had to do with music) experience it.
Flow, as summarized by Micheal J Apter, and theorized by Csikszentmihalyi is related to Self Actualization. Flow, which is as the complexity of a task increases so do our abilities to complete the task and in doing so relieves stress. Self Actualization is characterized by utilizing one's abilities to the fullest extent (Apter, 1995). At least a correlation could probably be calculated as a positive direct relationship; if you got one, chances are good you got the other one too.
Flow, like Self Actualization, can occur during certain situations without remaining continuous to other aspects of life - just because you can write well (or experience "Flow" while writing) doesn't mean that you'll have the same feeling when faced with a math equation (for argument's sake, calculus).
When they talked about "Flow" in terms of the writer I knew the feeling, when I draw and or write (prose or poetry or even some papers) I cease to acknowledge my body. It's what I'm supposed to be doing, and nothing exists.
However, another activity I enjoy is tutoring (Psych stats in my case). As Professor McGall put it, it's a feeling of congruity, "One with the universe", I don't cease to exist, I am very aware of myself and my tutoree. Or when I'm doing leg work for a study - once again, I truly love the activity but, I am very aware of myself and how I am interpreting what I am reading/doing.
In these examples, I feel, in my unprofessional opinion are the differences between "Flow" moments and moments of "Self Actualization"; where flow is something deeply personal and internal, self actualization is more external in nature. Flow relates to the activity, and self actualization relates to the self and the environment.
Apter, M. (1995). Complexity, Flow, Evolution, and Happiness. PsycCRITIQUES, 40(5), 430-432. doi:10.1037/003633.