3 years flushing. Metal fillings. Never a problem.
Deworming and colon cleansing - that's a sensible start. You don't necessarily want to do everything at once.
Can things get worse? Consider you are stirring up toxins and critters that have been sitting there. So, yeah, things could get worse. That's why you want to be sensible and keep things moving - through colon cleansing and just drinking water.
parasites can be microscopic, so you may never even see anything.