The magic is drawn from the life source of the dragon. The only people who could ever use magic without a dragon are the ancient species of elves that have long since faded from existence. Using spells, will wear you out. First you'll feel tired, physically and mentally. If you overdo it further, you'll feel sick, fatigued and unwell for a few days. Even further, you'll collapse. Further, you'll risk injuring your mind and your ability to remember things. Once you've worn your body down to the point of collapse and memory loss, your next step is literally sucking the life out of your dragon and doing serious damage to the length and quality of your own life if you survive the intense spell.

The basic magicka you'll work on with Merrik once you've gotten to training will leave you tired. But he'll help your characters build up a tolerance, magical endurance in a way :)

Does that help?

P.s. The magic will be explained as we go through the training IC but as always, feel free to keep the questions coming :)