underactive thyroid
"When I was not on any thyroid medication and when I was on Synthroid, I felt lethargic, mentally slow, uninterested in life, appathetic, at times depressed, I had no energy for doing anything, nor did I have a desire to do anything - especially interacting with people (this felt overwhelming), I also had unwanted weight gain.  When I finally switched to NDT, within a few days of raising my dosage to current level (4 grains), I noticed a huge difference in my personality, I started to enjoy listening to the radio in the car again and singing like mad (I hadn't even noticed that I had stopped doing that before), and I started to care more about friendships, going places, being part of activities, I stopped feeling depressed and I lost weight!"