Came from the slave days, and was considered a medical disease which needed curing if a slave was wanting to escape. So, metaphorically speaking, this word can be used as a noun if you feel trapped and ache for escape. on Travel quotes quotes
'I'm drowning and you're standing three feet away screaming "learn how to swim! - this is how being depressive must feel like. Horrible feeling for the screaming person as well - I know what I'm talking about.