Stretching when you are sick feels good because you are alleviating muscle tension and discomfort that could be related to the sickness. You are also increasing blood flow around the body, which may help immune cells get to the site of infection more effectively.Stretching when you are sick feels good because you are alleviating muscle tension and discomfort that could be related to the sickness. You are also increasing blood flow around the body, which may help immune cells get to the site of infection more effectively.