How do I explain my depression when everyone thinks I'm such a happy and positive person?

It's not about the way you present yourself on the outside, but rather the way you feel on the inside. If you feel sad or empty inside, you can still fake it on the outside sometimes. Just because you put up a good front doesn't mean you really feel that way. Think about actors - they don't always actually feel the emotions that they portray, but they fake it. A lot of people hide negative feelings because they don't want others to know or they don't want to bring down the mood or they're trying to fake it until they make it.

Nice Question! I would explain that depression is a complicated disorder that is not easily controlled, especially when things occur in life. Explain that Depression is caused by dysregulation and chemical imbalance of the brain and therefore, everyday maybe different. I would ask them to be patient and in between times you can still be a positive person.

Say that you might seem one way on the outside, but that's not how you feel and that's not how things are on the inside - explain what your depression feels like as best as you can with your words.

Masking emotions with "happy behavior" doesn't really change the deep emotions lying inside! While key symptoms of depression can be lethargy, disinterest, etc. that doesn't mean that the absence of those symptoms change whatever is going on in your head.

This is how I would explain it, by you always fake a smile. You always "act" happy by faking a smile, then you a sad.