This is actually a great question.
My personal experience of burnout in myself, and having seen it in others, is that it affects mood in ways that go well beyond productivity.
When people are burned out there aren't just not getting things done (and often they continue to perform on basic things like attendance), but they're grumpy, miserable, convinced everything will fail, and often dodge responsibility.
it feels more like something passive aggressive, whereas plain lazy people will just fade into the background.
taking a rest isn't enough to resolve burnout either. my experience is that it can take many many months for people to recover from severe cases, where there has been a lot of stress. some people can be broken forever.
laziness is actually kind of weird, and when i see laziness it is often either demotivation or procrastination.
Individuals will procrastinate because they aren't equipped to manage the tasks that come up in their work, due to missing mental skills or a lack of a sense of empowerment or responsibility.
Most people actually want to succeed and deliver in their work and are not consciously just not doing stuff. if given bite-size tasks they know they can complete they'll often attack them with gusto - but when they get larger more inchoate tasks they can struggle.
This is one of the more difficult issues to resolve as a manager, since the individuals themselves are generally not equipped with sufficient self-awareness, since they'd otherwise have resolved it themselves.
If you are asking if you yourself are being lazy then you need to consider how you relate to the work you aren't doing that you think you should. do you hate it? do you feel it is someone else's problem? do you feel that, no matter how you do it, you will get in trouble or fail? do you actually not know where to start? all of these are natural and come up in some circumstances, but knowing why you're not doing them will help you decide what might be causing it.