If you are feeling lassitude, you're weary and just can't be bothered. Couch potatoes make lassitude into an art form.
Lassitude might sound like latitude, but the two words don't mean the same thing. Latitude describes the distance of a particular location from the equator. Lassitude is the weariness you'd experience after attempting to run a marathon around the equator. Lassitude can also describe a lack of interest, like deciding you'd rather lie on your couch than run that marathon along the equator.