OP, though I know this is an old thread and you probably won't check this again, I would like to let you know that you're not alone in your problems. I'm in a very similar situation (i.e. major depression), except I chose to finish the classes I was taking, and consequently did horribly in them. I, too, decided to take some time off and I'm currently in a LPN program. Not the best choice I've ever made. However, I wanted to mention to you that perhaps you could do a similar lower-level health care related program, depending on the length of time you are planning on taking off from your undergrad education. Though the LPN program I'm currently in is a complete joke in terms of the quality of education, it did boost my confidence, as it showed that I was obviously capable of more difficult programs of study. If you don't want to take much time off, you could take a phlebotomy class.
Good luck to you.
Good luck to you.