I'm afraid that I might have a mental condition

I'd like to go and see a doctor to get a real diagnosis, but I'm not sure what I should make the appointment for. It's as though some mornings I'll wake up feeling so magnificently happy, like I just want to go to all of my classes and do all of my studying and go to work and talk to old friends I've had fallings out with. I almost feel high. Other times I've felt really scared, like afraid for my life, except I don't know why and theres nothing that I can do about it except shake and cry. And then the feeling subsides into normality, and in the next few days or so I spiral into a dark helpless depression and anger and sadness where all I want to do is eat or vomit, or punch a brick wall or cut myself, or sob uncontrollably or ream a close friend. And then there are in betweens where I just don't give a fk. I'll drink myself into oblivion or hook up with multiple guys who are all in love with me. I despise all of them, but I do it anyways. I have horrible anxiety, to the point of having chest pains at times, and sometimes I have insomnia, at others I can sleep all day long. What could be wrong with me?