In gameplay, when a character hits 0 MP, nothing really happens except they can't cast spells until they regen a bit.
In reality, it is possible to keep casting after hitting 0 MP, but the harder you push yourself, the more in danger you are of suffering mana burnout.
Pushing past that point starts as a headache that grows in severity the harder you push. Go too far, and you'll pass out. Passing out at this point means moderate to severe mana burn; stopping at the severe headache stage means it will probably be mild to moderate.
The effects of mana burnout can vary, but the most common symptoms are fatigue, fever, and temporary loss of magic ability. Severe burnout can leave a person unconscious for days, mild burnout might be nothing more than an especially long-lasting headache and a general tiredness.
The only cure for mana burnout is time. Drinking a mana restorative is a bit like putting on armour after you've already been stabbed. It'll keep it from getting worse, but won't fix the problem that's already there. Recovery time varies based on the individual and the severity of the burnout. Generally, any ability to cast spells is lost until the burnout has faded. This is not a hard and fast rule, and some people may still be able to cast during mild or mostly-recovered burnout, but even when possible it's still considered to be a bad idea.
Mana burnout
In reality, it is possible to keep casting after hitting 0 MP, but the harder you push yourself, the more in danger you are of suffering mana burnout.
Pushing past that point starts as a headache that grows in severity the harder you push. Go too far, and you'll pass out. Passing out at this point means moderate to severe mana burn; stopping at the severe headache stage means it will probably be mild to moderate.
The effects of mana burnout can vary, but the most common symptoms are fatigue, fever, and temporary loss of magic ability. Severe burnout can leave a person unconscious for days, mild burnout might be nothing more than an especially long-lasting headache and a general tiredness.
The only cure for mana burnout is time. Drinking a mana restorative is a bit like putting on armour after you've already been stabbed. It'll keep it from getting worse, but won't fix the problem that's already there. Recovery time varies based on the individual and the severity of the burnout. Generally, any ability to cast spells is lost until the burnout has faded. This is not a hard and fast rule, and some people may still be able to cast during mild or mostly-recovered burnout, but even when possible it's still considered to be a bad idea.