I can sell you some if you *really* want

Anyway, burnout isn't limited to just if you don't get sleep or just if you don't enjoy what you're doing. I've only experienced it a couple of times, and both times it came from doing intensive study over several days despite getting 8 hours of sleep a night. The mental energy needed to sustain study and the stress of it is just ridiculous (although tbf I was doing really long hours that I wouldn't recommend to anyone). Burning out from staying at school and studying until 6 probably isn't going to happen quickly, unless you then go home and keep studying for a few more hours.
The upside is that it's relatively easy to clear a burnt out state, you just have to do no study for a few days. I wouldn't get too worried about it if you're feeling fine and not pushing yourself to keep working through a period of tiredness etc. Just make sure you're on top of the situation rather than getting buried under a bunch of work
Also
I'm going to take a stab here, the effects of burnout have been researched and it is shown to actually exist, but I think it is all mental and it's all a big myth really, if you really love what you do then you should have no problem doing it for long periods of time right?
I know that it exists, but as far as I know, it's mental right? Not physical - it means that we can change it by changing our beliefs, the way we look at things (perception) and the way we respond to things, I'm not saying I'm right - but it's just something I was thinking about
This is wrong, saying something is "mental" and is thus a "myth" is not a good understanding of what's going on. You can't just "change your thinking" and snap out of it. It's similar to some types of depression in that sense, since it's fundamentally a chemical problem in the brain. If you've reduced your 5HT3/serotonin or dopamine levels from studying 12 hours a day, you can't just snap out of it. I don't want to get into the neurobiology, because I hate neurobiology, but stress and burnout cause pretty fundamental changes in how the brain is working that you can't just get rid of.