It's an excellent question, actually. I treat thyroid patients, and I see people all the time who were told to take antidepressants for their "depression", when really their complaint was that they were too tired to do anything - because of their thyroid problem.
The way I see it:
TIRED - would like to get out and do things, but it all just seems like too much effort. Not unhappy, necessarily, although may be frustrated that their physical limitations are keeping them from things
LAZY - I really have trouble with this as a concept. I think most people who get labeled as lazy, are really actually tired. We all know certain super-energetic people who can run rings around the rest of us - they don't have superior minds, they have superior health. Conversely, I think most "lazy" people are suffering from some medical condition that makes everything harder.
DEPRESSED - depression causes anhedonia - the loss of the ability to take pleasure in things that would normally be fun or enjoyable. Sadness OR irritability OR anxiety may manifest. Obsessive intrusive negative thoughts may occur.
