Mood swings, chest pain breathless.

I have been getting mood swings since 2-3 months back as sometimes I feel so happy and sometimes I feel very low. When I feel happy I find all the solutions to my problems and I think that life of full of good things, bad things don't stay for long. But when i feel low even the positive things seems to be very demotivatonal. I try my best always to keep me in postive way but as the low mood attacks me I dnt feel anything good. I feel fear of dying. I feel like now immediately am gonna die. My body becomes cold and i feel terror and starts shaking. Suddenly at any time i starts crying for no any reasons. I want to scream, and suddenly my tears stop and sometimes i laugh too for crying. Sometimes while laughing i starts crying. I am really very frustrated with this things. I feel irritated. I dnt like to talk with anyone. I have found myself several times just staring at wall without thinking anything for some minutes. I feel a strong pressure on my head.