The severity of the Herx reaction is often an indicator of just how much toxicity there was in the body to begin with and is an indicator of the effectiveness of the treatment. It is actually a sign that the body is restoring itself to good health. There is differing data on the timing of a Herxheimer reaction. Some data indicates that it usually occurs between four and 24 hours from the onset of treatment. Others note that between Day 3 and Day 5 of a treatment program is often when the reaction is most noticeable.