A happy moment is one, of which one seeks repetition. Repetition can, but may not occur because of the original trigger of happiness. That trigger occurs immediately before, and usually is an accomplishment. Repetition may also occur with replaying the memory of the trigger and the ensuing happy moments.
Happy moments may leave either contentment or sadness in aftermath. Sadness occurs when one assumes happiness to be the minimum acceptable standard for living, and lack of happiness is seen as a trough, or a deficit. Contentment occurs with the awareness that happiness is not a given, but is earned along with existence of appropriate conditions (e.g., absence of overwhelming pain).
Ecstatic is a moment, the intensity of which consciousness cannot fully capture, and memory cannot retain. Ecstasy* being a novel and/or rare occurrence, may leave happiness in its wake. Ecstasy overwhelms the consciousness, and consciousness can never be prepared enough for ecstasy. The loss of control felt can be discomforting. Hence, I do not seek ecstasy repeatedly.
*I was not talking of the substance! ;)