I recently had the same issue with a female Veiled that had laid a large infertile clutch. Her problem was calcium deficiency (understandable after forming all those eggs).
I treated her with an oral liquid calcium for about two weeks, during which her tongue strength returned. Calcium is a likely culprit because it is crucial to muscle action (needed for transmission of messages by the nervous system), so a deficiency in it can lead to a non-functioning tongue or other muscle co-ordination problems.
But other nutrient imbalances can also cause similar problems. Low potassium is another one that causes muscle movement problems like low calcium.
Since your cham has had a bout of not eating, and also parasites, it is quite likely that not all the necessary nutrients were being digested. If I were you I would up the dosage of supplements you are providing for a little while (calcium as well as multi-vitamins), and make sure your feeder insects are well gutloaded.
I would also try hand-feeding whilst there are tongue issues - try to get the cham not to use its tongue until proper tongue action has returned (even if it doesn't actually eat from your hand, at least hold a cup/saucer with superworms/silkworms up close to its mouth). The worst possible scenario would be if the tongue went out and then couldn't retract. That could be a life-threatening situation for the cham.
A trip to the vet would be a good idea too - maybe you could have his calcium levels checked out.
