There are different types, I've had a fair bit of experience with depression.
I've suffered with it. I'm generally a constantly happy go lucky always smiling person around people but I've been at places where I've not been able to peel myself out of bed for days on end, felt like crying or so far removed from myself it's been unbeleivable, mixed up with an inability to see that something is really wrong.
My partner also suffers with it and has had medication for it in the past, as has my dad. Medication helped her, drink was my dad's answer, and I suppose my method is withdrawl and reflection and putting it on myself to make a change with the only place I really speak of it being within the anonymity of forums etc.. It's been hard and I can't judge others who couldn't do this, because for all I know, they have it worse than I and can't.. Generally no two cases are the same so it's hard to dismiss someone who says they do have it - but often the people who wave it about as an excuse, generally, just need to get a grip in my experience. That's not to say some people don't openly say they have an issue to friends and family, but it shocks me how selective some people are when it comes to when and how they will show it..