Impaction is where there is a blockage of the intestines and poop cannot get out. The poop is stuck in the body causing pain and finally sepsis which is fatal. There are a number of things that impaction is blamed on including eating mealworms with high chiton in their exoskeleton to ingesting substrate. As there are chameleons that love mealworms and chameleons that pass inorganic material without and issue the story gets more complicated. It is suspected that impaction occurs not because of what was ingested, but that the environmental condition were off. The most likely culprit is the body not being the right temperature so it did not work that well. Other reports include having a parasite load so massive that it actually started impeding flow in the intestines. I would have to research this to verify it was true as amassing enough microscopic organisms to block the intestines would be an amazing situation. Though when we get to parasitic nematodes (worms) there are some worms that can get massive enough that one can block the intestines.
The chameleon will show internal distress by being lethargic and progressing onto eyes closing during the day and sinking in. There can be an appearance of being bloated.
This picture is of a female Furcifer pardalis in dystocia (egg binding) distress. This is where there is something preventing eggs from getting from the oviduct and out of the body to beg laid. This not intestinal impaction, but it is the same dynamic (a mass of something is not able to exit the body as intended) and the external appearance and signs of distress are the same.
Bring your chameleon to the vet to have them help the blockage pass. This is a life threatening situation.
For there to be an intestinal blockage something has gone wrong. You will get a clue from the vet as to what was causing the issue. Was your chameleon eating soil? This is a sign of lack of minerals in the diet. Was it a huge parasitic infection? Be careful killing all of them at once and sending your chameleon into septic shock, but you will have to work with your vet on a plan to clean up the digestive track. Was it a mass of mealworm exoskeletons? Although mealworms should, at most, be a small part of a varied diet, your chameleon should be able to pass the waste. Check your temperatures to ensure they are warm enough.
There does need to be a correction, but this must be appropriate to what caused the condition.