Can someone help me figure out what's going on with me?

I just don't understand what's going on with me anymore. I'm a senior in high school, in all accelerated and advanced placement classes, am going up to Boston in the fall for college, have so much ahead of me, but just see no point in anything at all anymore. I cry myself to sleep every night. I could care less about this 10 page paper for my AP English class due in the morning. I don't even want to show up to work tomorrow either. I find myself feeling happy one moment, and completely miserable the next. I forget absolutely everything. I'm seriously behind on all my schoolwork and projects. I will legitimately sit down in my room to do my work, and just sit, for hours on end, and not do any of it. Then go to bed, not caring anymore that nothing is done and go to school late and just tell the teacher "Sorry, I didn't do it." I cannot remember what I did yesterday, let alone this morning. I don't want to see anyone. I never want to talk to anyone. I envision the world without me. I can honestly say if my best friend died right now, it wouldn't even phase me. I try to explain this all to my parents, they just say I'm being lazy and have to get my act together. Please let me know that this is just a phase, it's been like this for months.