Hugs to you, Melissa. Between the decreased concentration, impaired memory, and tendency towards self-hatred, depression is very good at convincing us that we aren't very smart. Studies have shown, however, that depression doesn't really touch problem solving ability apart from its effects on memory and attention. So, no matter how dumb you may feel, you actually are just as intelligent as you ever were. You may need to be creative to overcome any lasting memory or attention problems, in addition to any depression-related anxiety. But you can do it.

I also used to be a straight-A student, until I was hit by an intense depressive episode during my senior year of high school. Like you, the drop in my grades wasn't dramatic; I went from all A's to half A's, half B's. It was enough, however, to make me feel like an idiot. Enough to discourage me from taking some math and physics classes that once upon a time I would have been capable of handling... So I can definitely relate, though my depression wasn't as severe as yours (I've never been hospitalized).

Really, the fact that you managed to get mid-high 80's when you were severely depressed is quite an accomplishment. Many people would fail all of their classes if they became half as ill as you were.

I'm not sure how things work in Canada, but in the US people can pass a test called the GED and be granted a high school diploma. Perhaps you could look into something like that, which might get you your diploma faster and with less hassle. Also, don't give up on your dreams. If you want to go to university, go. And spit in depression's face when you graduate!

What do you want to study after high school?