I can't believe this!!!!

I just got a call from my work . Apparently I was supposed to be there this morning at 7:48am (I know, weird hours) for a shift. I didn't even know about it!!! I called in and said that I couldn't come in because of appointments (counsellor, support group, then doctor)...my immediate supervisor did not sound happy. He said that the shift had been on the schedule for at least two weeks. What am I supposed to say to that? I feel like such an incompetant moron.
But I swear that my manager said she would let me know if she gave me extra shifts ahead of time(or at least I think she did???) apart from my regular job. I KNOW I'm going to get pulled into my bosses office on Monday and reemed out. I am sooooo scared.
I know this happened due to my lack of focus and my depression...maybe I can get a doctors note? Oh Lord, I am so scared...please help me....I am so afraid of the repricutions of this!!! :(
Could you guys please keep me in your thoughts and prayers (if you believe in God) on this matter? My boss does NOT understand mental illness at all. She has the whole "Just get over it" attitude. (Even thought she claims to be a Christian and she lost her husband early in their marriage - you'd think she'd have more compassion - go figure).
I can't believe this!!!! I hope I did the right thing by saying I couldn't come in due to appointments...that can count as sick time...I hope? I am soooooo scared. Ack!
Lord, please help me.
When it rains, it pours, doesn't it?
Shebee