It's the same as relationships. I feel all such extreme emotions with respect to people too. In a single day i will feel full of love for them and I would also get awfully upset with them. Imagine this level of variation - I can go from - being willing to give my life for someone to taking their life - kind-of-state - in a matter of few hours....AND NO - i have never actually gone that far as to hit or harm anyone.
I feel the number of people suffering from such issues is huge - perhaps much higher than we can anticipate. And worse is that half of them don't even get to know whats going on! Everyone around keeps telling them to cheer up and stop being what they are going through.
I can very well relate to this. Family and friends say all motivating things to make me feel good besides showing me that they are with me and supporting me. It helps but briefly. At times it works opposite as well. That - do this do that - kind of pep talk is what i detest the most. That makes me feel inadequate. Why do they assume i wouldn't have tried or done anything at all!