Is it possible for a normal healthy woman or anyone for that matter to involuntarily just stop breathing? during the day, other than sleep apenea?

Breathing: Its usually not normal could be a autonomic response or panic response, needs to be evaluated its probably benign but could do get work up done.

Yes : But if you are doing it during the day i would have a nighttime polysomnogram done to make sure you do not have sleep apnea, since even skinny people can have it and forgetting to breathe during the day can be a symptom of it.