Tyson never gets 'ill', he gets fevers.
If he catches any form of sickness it becomes a fever almost without fail, if it is anything more than a cold or a headache.
His fever normally breaks after two days.
The severity varies depending on what he actually came down with. Sometimes he'll just be running unhealthily hot, but power through it. Other times, he'll be unable to lift his head from his pillow without feeling lightheaded.