This poem is excellent with it's wording and simplicity. There is depth in each line written and I am going to add it to my favorites list. To the poem itself.
I'll get a small nitpick out of the way first. It seems like throughout the poem itself you didn't use capitalization at all (I feel it is because you wanted the reader to feel sadness which you portrayed well.) You made the character feel small and non-existent so I must point out that for consistency sake, the I's in the poem should be lower case as well.
The character within the poem itself is well written with sadness, I think with the use of "I" you are writing this about yourself. The good thing is that this could imply many things. I'll go with what is in front of me though, you feel invisible in this world, and that leaves you feeling cold, lost, depressed.
I love how this poem reads as one full line within multiple and it reads well without punctuation. It is like you are feeling all these things at one time and you don't know how to handle it all. The feeling of dread hangs in the air.
The ending of the poem is my favorite part because the two major words are connected. Invisible and ghost work well together in a poem. They also work well to give the reader a feeling of death and that is what depression really feels like.
I wouldn't change anything besides what my opinion is in the nitpick paragraph. :)