So, the speaker of "I Am" isn't a raving lunatic or anything, but knowing what we know about Clare we can't help thinking this poem gives us at least a little glimpse of what the world looks like to somebody who's on the verge of a mental breakdown. People start to seem different, sounds aren't really recognizable, and strange things like "woes" become visible. The poem doesn't really say anything about how this happens, but it's possible that the speaker's extreme loneliness has something to do with his state of his mind.
Madness makes us see things that we wouldn't otherwise be able to see, which could actually be a good thing. The speaker, for example, appears to be able to see his woes rising and vanishing, which sounds pretty cool, if you ask us.
There are degrees of madness. One doesn't have to be crazy to be a little mad. Take the speaker; he's clearly starting to lose it, but that helped him to write a great poem.