Depends on what you mean by "burnout". It's nothing worse than overexerting yourself physically and having to deal with being sore for a few days. Don't get me wrong, magic comes with its risks, but the dangers are easy enough to avoid if you aren't stupid about casting. It's like driving a car, I guess.

[She's gotta have cars in her world, right? It's so hard coming up with universal metaphors!!]

If you're sick, yeah, it can be tougher to cast, especially if you're inexperienced. Same with being really tired or drunk or something. Anything that affects your concentration or your energy is going to affect how your magic casts. Having a cold or being a little sleepy isn't going to do much, but if you've got the flu or some shit, it's not a good idea to be messing around with serious spells. You can still cast, but won't have as much control.