11. Decreased immunity or illness
Along with feeling run-down, you may find you get sick more often. You may also be prone to infections, mild illnesses, and upper respiratory tract infections (URTIs).
12. Weight gain
Exercising too much without resting enough in between can lead to low testosterone levels and high levels of cortisol, the stress hormone. These hormonal changes are often associated with loss of muscle tissue, weight gain, and excess belly fat.