Can a dental cavity make you feel sick and tired?

Yes: A cavity is an infection. Like any infection anywhere in your body, your body has to expend energy to try to defend against the infection spreading. Best thing you can do is see your dentist asap to have teeth and supporting tissues returned to optimum health.

Dental abscess: A dental abscess can begin as a tooth infection or a simple cavity. Eventually, dental abscesses can also make you generally ill, tired with nausea, vomiting, fevers. See your dentist for preventive appointment.