Grab him by the middle with just two fingers and pick him up. Does he hang rather limply? The only garters I have ever had that acted like that died. Although in the rare cases it did haplen i couldnt find anythiNg outwardly wrong with them. It sounds like plain old lethargy to me. The brown spots are probably scale rot. It sounds like he's not well off. Scale rot is usually bacterial though if I am not mistaken so I doubt fungal spray does anything. To correct scale rot all you have to do is keep him really clean and dry. Keep him on plain paper towel and change his water frequently. Do not allow him to soak until the wounds heal, any moisture helps the bacteria grow. It's possible that the scale rot went systemic and is now an infection that is internal, cycling through his blood. If it is that bad, the only thing that may help him is antibiotics.