I don't think it's that much of an either or type thing. I think there are a lot of factors going into laziness (just as their are for depression), and its more of a reaction/result than an action/disorder in itself.
I am lazy about some things. I'm sure everyone is, actually. As we all know, laziness results from disinterest, lack of motivation. Shit, motivation is complicated, too, theres a lot of things influencing it. When people don't do things because they don't want to, it can be because of disinterest, too much challenge (turned off by the difficulty... you arn't going to try to hard to do rocket science if you don't know how), not enough challenge (why bother if I know I can do it?), if you value/appreciate the work, or possibly just the nature of the activity, how it is organized (if something is set up poorly or in a way that is significantly uncomfortable for you as a person). Some laziness could be fixed by just sort of... recalibrating the task. For example, I had a science project last year that I didn't want to do. To get myself interested, I decided I would present it in an outrageous unique way by making it into a Twilight Zone-esque simulation asking the audience to imagine the world as my project needed. I made sure to find a lot of interesting pictures and comics, too. I might have spent slightly more effort on the presentation aspect than the information aspect, but it got me more involved and I did well.
I really think laziness can happen to hardworking people a lot, they just need to find a way to make it engaging, make it something they can commit to. I know that in my current issues with laziness (mostly related to english class) I would love to actually put effort in and work hard but find it difficult because I'm not very interested.
And I can really see how laziness could trigger depression... I get sad knowing I'm letting people down with my poor performance in school, and especially I'm letting myself down cause I know I could kick ass. I can see how that could, in some people, go to an extreme and consume their lives. Its sad.
Dissonance, I don't entirely agree with you idea that lziness is masked self destruction. I think there is truth to it, it happens with some people, but I think some laziness is replacing your obligated work with work that you find more rewarding, which isn't always self destructive. For example, not doing your work to eat doritos and watch football is probably self destructive, but if an artist skipped their obligated work to paint, it wouldn't be self destructive, it would just carry a negative consequence for the sake of learning and doing something more rewarding and productive to you.