"...you're exhausted in spirit as opposed to exhausted from being depressed."
A good observation!
For example, people in the helping professions are known for job burnout. It is a spiritual exhaustion and they say it takes months or years to develop some unhealthy thinking like apathy and being cynical towards their clients or towards their job.
But BP's have a physical ailment. It's a energy issue....our brains are wired differently and misfires like a bad spark plug.
When I was in my depressive state I could feel my frontal lobe "hurting"...I could feel it! I could not physically get out of bed. It took so much effort to get myself going. My psychomotor was slowed down and I felt it. I felt physically ill. I had to force myself to eat something, go to the gym and go to work.
Someone won a court case....interesting reading.
Fitts v. Federal National Mortgage Association
http://pn.psychiatryonline.org/cgi/content/full/37/8/23
I think being burnt out and depressed can present themselves in a similar way but they're both different things. You can become listless for example from both. It's a very different feeling however when you're exhausted in spirit as opposed to exhausted from being depressed.
People can get stresed out but depression and bipolar are very specific but if you had difficulties with work or didn't recieve the accomodations you needed it could have triggered episodes as stress can do that.