How do you tell the difference?

I've only been feeling bad for the past two days but promised myself that if I got seriously depressed one more time I would try mood stabilizer (then again, have made this promise many many times...)

Things were going great and then had a few very minor conflicts with family (common) which seemed to really get me down for some reason. Since then I've been much more sensitive and angry and just want to be quiet and alone.

Then last night I was reading some old medical records from when I was a teenager (for a book project) and saw some stuff that bothered me - like notes from my psychiatrist about him trying to get my mother involved and her not taking my problems seriously or returning calls etc. he even suggested I be voluntarily hospitalized but I never knew this until now. My mom is amazing and I know she feels guilty about this now, but I still feel angry about it because I was made to feel like a faker/drama queen and haven't been able to take my problems seriously since.

My heart is aching in that familiar way, I am unmotivated, and rather hopeless when I think about the future. I still enjoy reading tho, and am able to go to work etc.,, so that's good.

I guess my question (buried in my venting) is: where / when do you draw the line between a bad mood and an episode?