During a massage, the physical manipulation of the muscles and tissues can help release built-up toxins, such as lactic acid and metabolic waste, into the bloodstream. This can cause feelings of discomfort, headache, fatigue, or nausea, which is commonly referred to as a "detox reaction." However, this is a normal and temporary response to the massage therapy, and the symptoms usually resolve within a short period of time. It's important to drink plenty of water after a massage to help flush out the toxins and maintain proper hydration.