I don't usually hear this unless something is wrong.
It is common to have a modest increase in prechelation symptoms while on round; however, some people get improvements in some symptoms as well.
For example, a close friend has more fatigue and brain fog but she sleeps better.
Strange symptoms can occur when people don't take enough antioxidant protection, or when they still have Amalgam remaining, maybe under a crown. Also symptoms might build if you are not taking doses frequently enough or are skipping night doses.
For example //www.curezone.org/forums/fm.asp?i=1007420#i