I want to resign from my job

Here I am as usual, fallen prisoner to my own crippled mind.
I am feeling lousy and I have fallen into the trap of not going to work.

I did not go to work last Tues and Wed, and have dragged myself to work on Thurs and Fri as I can't bear the thought of letting my assistant down.
I managed to stand in front of 24 people on Sat during my study launch and presented to them, confidently. I received good feedback and I felt good.

But I felt inadequte too and have been very down since yesterday.

I am at home typing. I didn't go to work again. Think HR is going to talk to me soon.
I just can't control my minds and mood. I really really feel very very depressed. It's me, but I can't get out.

I want to hurt myself, yet I don't.
I'm caught in a catch 22.

I'm afraid I may have to leave this job as I can't cope. but it seems so weak.

I am very down and my tears are stuck. I can't cry.
I really really feel horrible. want to run away.

what shd I do?