Honestly, I find the assignments that end up most rewarding (and not being another chore) are the ones that come from the heart and sort of leave you vulnerable I guess. I'd say go for it, and like you said if it puts you in an awkward situation you can always say it's fictional. It's creative work though, so I don't think it would be much of an issue really, iylu shouldn't have to justify. Your professor would probably appreciate that you'be chosen to write about something that's so personal, especially that it's how you get your best work done usually.