It sounds like you had a wonderful time with your friend while she was feeling "up." She showered you with attention. I'd love to have such an experience. Maybe you should just be happy with that. As Dr. Seuss says, "Don't cry because it's over -- smile because it happened." I personally don't go from hypomanic to depressed within a day. For me it takes weeks. But there is a wide variety in how people experience their bipolar. If your friend really does have bipolar, she will probably be "up" again so you can look forward to that.