I'm sorry. Depression can hit anyone at any time. It seems like once you've been diagnosed with depression it never REALLY goes away. You may go into "remission" but it's always in the background waiting to attack at any moment.
Talk to your doctor, and get back on your meds. It's possible you have clinical depression. Ask him about that -- ask him if it's "major depressive disorder" also known as clinical depression. If that's it, you'll have to STAY on medication permanently.
But get back on the meds. You can't go on feeling like this. It's dangerous for your mental AND physical health. God bless and please take care. keep us posted. Hugs, Lee