A symptom of depression: Helplessness

Last night, after finishing that last post, I went to bed. As soon as I turned off my light and crawled under the blankets, I lost control. I couldn't stop myself. I was sobbing, pulling at my hair, choking on tears. It went for a few minutes until I was gasping for air; I couldn't make myself breathe properly. Finally, I got air into my lungs and forced myself to calm down so it wouldn't happen again. I just felt so helpless and alone.
I needed to talk to someone but I couldn't think of anyone that I trusted who would wake up if I called them. If you have someone who is willing to wake up at 1am and listen to you cry on the phone, don't ever let them go. I wish I had someone like that.
When I woke up this morning, I didn't feel all there. I felt like part of me had disappeared.
For the last couple of weeks, in the back of my mind I've known that I'm not been alright. It's more than being sad and feeling sorry for myself.
Just before writing this, I googled 'symptoms of depression'. In a list of 11 symptoms, I identified with 10. That was scary but what was absolutely terrifying was when I googled 'symptoms of anxiety', I found I had all the symptoms of generalized anxiety disorder (GAD) and that anxiety and depression are closely linked.
Now I realise that I was just reading this off the internet and that I can't diagnose myself but the way I've felt these past couple of months, it just doesn't seem like a coincidence. 
My problem is what do I do now? Do I tell someone? Do I keep it to myself? I just feel so alone in all of this. Why is there so many things wrong with me?
~Wannabe