I've had problems with depression and I'm currently dealing with my boyfriend's bout of depression. Point blank, depressives are negative. In their head, nothing works out so why try? Normally, you stop feeling "good" emotions - even down to feeling happiness with someone you are truly happy with. In my case, I start to feel kind of numb. In my boyfriend's case, he starts to find fault with everything and gives up easily under the notion that it's not going to work out anyway. We both, unfortunately, get the lack of motivation - his currently is infesting in a ugly way with his job & it's manifested in me by putting off going back to school. Depressives can also exhibit hypocritical or uncharacteristic behaviors - Both my boyfriend and I will have the tendency to not make plans, break plans, use undefinitive words when depressed & it's completely the opposite of how we are when not depressed.
Laziness? I'd define it more as not feeling like going into work after a night of drinking or not finishing your tasks because there's something better to do. Not going into work because you've given up on life or not finishing your tasks because you're so distracted by negative thoughts is depression.